Continuous spawning in the cirrate octopods Opisthoteuthis agassizii and O. vossi: features of sexual maturation defining a reproductive strategy in cephalopods

The reproductive strategy of the cirrate octopods Opisthoteuthis agassizii and O. vossi (collected off Namibia from 1988 to 1990) was analyzed. Ovarian oocyte size frequency analysis for both species revealed continuous egg production over the entire adult life span. Mature eggs were stored in the single oviducal gland and distal oviduct, but oviducal gland fullness was not related to body size (p>0.2). All O. agassizii male specimens from 95 to 5400 g total weight were sexually mature, as were all females from 190 to 1650 g, indicating that considerable growth takes place after the onset of sexual maturity. Continuous spawning is defined as a single, extended and continuous period of egg maturation and spawning. This model of reproductive strategy is previously unreported in cephalopods. All O. vossi male specimens from 750 to 3050 g total weight, and females from 800 to 1300 g, were sexually mature. Mature males and females of both species were collected in all seasons of the year. The adaptation of cirrate octopods to non-scasonal deep-sea environments is considered. The sexual maturity characteristics of males were analyzed, and examination of the spermatophore revealed opercular structures previously unreported in cephalopods. For females, the micropyle of the eggs are described and the mineral analysis of the egg shell disclosed that sulphur was the major element present.     

Encapsulated development of the marine prosobranch gastropod Nucella lapillus

Nucella (=Thais) lapillus (L.) develops to the juvenile stage within an egg capsule. This study was undertaken to investigate nutritive and bacteriostatic properties of the intracapsular fluid for this species. Capsules were collected intertidally at Nahant, Massachusetts, USA, in the summers of 1982 and 1983. The average capsule contained only 1.1 l of intracapsular fluid per embryo. A statistically significant correlation was observed between capsule height and number of developing embryos contained therein, although the number of embryos per capsule was more closely related to capsule volume. Total dry weight of encapsulated, shelled embryos increased exponentially as a function of shell length. However, weight increases may be entirely due to shell calcification; the average dry tissue weight of shelled embryos was significantly below that for pre-shelled individuals, suggesting a net loss of biomass during development. Aliquots of intracapsular fluid failed to inhibit the growth of the 13 bacterial strains tested. Despite the above results, pre-shelled embryos generally survived only several days following their premature removal from egg capsules at 12°C. Shelled veligers were reared outside of the capsules with no apparent ill effects. An explanation for these survivorship results is elusive.     

Two modes of development in the morphospecies Crepidula dilatata (Gastropoda: Calyptraeidae) from Southern Chile

In Chinquihue Bay, a sheltered locality in Southern Chile, female Crepidula dilatata Lamarck brood egg masses which differ in intracapsular development. In some, all eggs develop and are hatched as free veliger larvae (indirect development). In others, only some of the eggs develop and hatch as young adults (direct development), the rest being consumed as nurse eggs. Two possible interpretations are considered: intrapopulation variation of developmental pattern in a species, and the coexistence of two sibling species. Stages of the intracapsular development are described and illustrated. Fecundity varies according to size of the female. For females brooding eggs with indirect development it is estimated at between 3840 and 85575 embryos per spawn; for females with eggs undergoing direct development, embryo production per egg mass is estimated at between 70 and 812. A comparison is made between females brooding the two kinds of egg masses. Minor differences exist in adult coloration, shape of egg capsules, egg diameters, spawning season and their abundance and distribution in the intertidal. Brooding females with eggs displaying indirect development are significantly larger than those with eggs of direct development. The latter females form chains subtidally but not intertidally as do females bearing eggs with indirect development. On these females with pelagic larvae, chains frequently include sedentary males which reach large sizes. On basal females with direct development, chains contain mostly other females, suggesting that matings are temporary and by errant males. These results are compared with existing information in the literature for other species both in this genus and in other marine invertebrates. It is concluded that two sympatric sibling species with different modes of development are present in the morphospecies C. dilatata Lamarck in Southern Chile.Devoted to Dr. E.F. Kilian, Zoologisches Institut der Universität Gießen, FRG.     

Yolk testosterone organizes behavior and male plumage coloration in house sparrows (<Emphasis Type="Italic">Passer domesticus</Emphasis>)

Vertebrate eggs contain maternal steroid hormones in their yolks; and in avian species the concentration of these steroids vary within and among clutches. The organizational actions of these variable doses of maternal steroids in the avian egg, analogous to those regulating the development of sexually dimorphic traits, are little explored. In this study, we examined the organizational effects of yolk testosterone in the house sparrow, Passer domesticus, a sexually dichromatic passerine bird in which males are characterized by the presence of a throat patch or badge of black feathers that varies in size among males. We injected a physiological dose of testosterone or vehicle into eggs in the field, removed nestlings, and hand-raised them in the laboratory. At 5 months of age, we investigated treatment effects on plumage and behavior. Males that hatched from testosterone-injected eggs developed a larger badge than males that hatched from vehicle-injected (control) eggs. However, testosterone did not induce the expression of a badge in females. In staged dyadic encounters, both males and females hatched from testosterone-injected eggs were more successful at obtaining and defending a food source than individuals of the same sex hatched from control eggs. The results suggest that variable concentrations of maternal testosterone in the eggs of the house sparrow organize the expression of a plumage trait in males and behavior in both sexes.Communicated by J. Graves     

Egg laying and embryonic-larval development in the snail<Emphasis Type="Italic"> Thais (Stramonita) chocolata</Emphasis> (Duclos, 1832) with observations on its evolutionary relationships within the Muricidae

Oviposition and embryonic-larval development are described for the muricacean snail Thais (Stramonita) chocolata from the Southeast Pacific coast. As with numerous other muricacean snails, this species engages in communal egg laying, with females depositing egg capsules in clusters on subtidal rocks. Each cluster of capsules contains 100–150 pedunculate, ampulliform egg capsules, with each capsule containing an average of 2,600 small (130 m) eggs. Intracapsular development was followed using light and scanning electron microscopy to describe the successive embryonic stages of the species. Free-swimming veliger larvae of about 225 m length were released from capsules after 49 days incubation at 13.6°C. The planktotrophic larvae were cultured in seawater aquaria by feeding with pure cultures of phytoplankton, recording growth and form of the larvae. Larvae reached competence after 4 months at 22°C, at 1,450–1,740 m in size, and a few larvae were observed through metamorphosis and early definitive growth. The embryonic-larval development of T. chocolata coincides with the general characteristics of the ontogeny observed in other Thais species as well as of other genera of the Rapaninae such as Concholepas. This lent support to grouping these genera into a single clade. The lack of knowledge of the development of free larvae of Thais spp. means that we do not know whether these similarities also include an extensive larval phase as generally characteristic of other members of the clade. The mode of development may be useful in characterizing some clades of this family. Thus for example, the transference of some Thais to the genus Nucella (Subfamily Ocenebrinae) is supported by differences in the mode of embryonic development, which differentiates these subfamilies. Paleobiological data reported for Neogastropoda allow postulation of primitiveness in planktotrophic larval development compared to more recent developmental strategies such as direct development of different types, which characterize various clades of this family.Communicated by O. Kinne, Oldendorf/Luhe     

Biology,population dynamics and secondary production of<Emphasis Type="Italic"> Tylos europaeus</Emphasis> (Isopoda,Tylidae) on the western coast of Portugal

The biology, population dynamics, and production of Tylos europaeus were studied in two sandy beaches of the western coast of Portugal. At both sites, reproduction occurred seasonally, from April to July, with only one new cohort produced per year. Regarding population dynamics, cohort-splitting events were detected in males at the beginning of the reproduction period (April/May), resulting in two groups with distinct growth rates (fast-growing vs slow-growing males). Different biological characteristics were consequently detected in these two groups, namely regarding body size, lifespan, and contribution to the reproductive effort. Lifespan was estimated as approximately 3 years, for females and fast-growing males, and 4 years for slow-growing males. Cohort-splitting among males appeared as a possible strategy to cope with the highly male-biased sex ratios observed, which could lead to a strong male-male competition for mating. T. europaeus appeared as an annual species, with a univoltine life-cycle (one generation per year), and iteroparous females reproducing twice during their lifespan. Average growth production (P) was estimated at 0.082 g.m^–2.yr^–1 AFDW (ash-free dry weight) and the average annual biomass () (standing stock) at 0.052 g.m^–2, resulting in a P/ ratio of 1.58. These results produced baseline information for the construction of a population-dynamics model and highlighted the potential of this species as an environmental quality-assessment bioindicator on sandy shores.Communicated by S.A. Poulet, Roscoff     

Egg-capsule deposition and how behavioral interactions influence spawning rate in the squid<Emphasis Type="Italic"> Loligo opalescens</Emphasis> in Monterey Bay,California

Recent evidence suggests that, contrary to what was believed previously, most Loligo spp. females spawn multiple times and do not die immediately following a single spawning event. The present study used sustained focal observations of male/female pairs of the opalescent inshore squid Loligo opalescens Berry to examine the structure and behavior of near-bottom spawning groups. The study was carried out in a small area (10 km²) of Monterey Bay, California (36°36.1N; 121°53.4W), at depths of 25–45 m, using video cameras mounted on remotely operated vehicles. Behavioral observations were made primarily during daylight hours over known spawning beds in April and November 2000, and August 2001. Squid formed large aggregations in the water column where pairing occurred. Most commonly, only small numbers of active spawners were found at the substrate depositing egg capsules, and the mean operational sex ratio in the spawning groups was 1.87 males:1 female (range=1.0–8.5), although the ratio fluctuated rapidly as roving lone males joined and departed from the small spawning groups. On average, females (n=40) deposited 2.67 capsules (range 2–7) per focal observation at an average interval of 8.47 min between depositions (n=67). Following deposition of the capsules, females broke away from their consort males and jetted upwards to rejoin large schools located many meters above the substrate. Egg-capsule deposition was often interrupted by lone males seeking a mate, or by the approach of predators including fish and marine mammals. The results suggest that most of the communal egg beds in southern Monterey Bay are built up slowly through daily intermittent spawning, not in large big bang reproductive events as often depicted for L. opalescens.Communicated by J.P. Grassle, New Brunswick     

Sperm competition in the damselfly Enallagma hageni Walsh (Odonata: Coenagrionidae): benefits of multiple mating to males and females

Summary Sperm competition was investigated in the non-territorial damselfly, Enallagma hageni. Using irradiated (sterile) male techniques, the last male to mate was found to fertilize up to 95% of the eggs of the first clutch laid after mating. Dissection of females collected before, during, and after copula showed that a male removes a maximum of 87% of the sperm by volume of a previous mate. These data verify an earlier estimate of lifetime reproductive success in this species which was based on mating success, and suggest that indirect dissection methods offer minimum estimates of sperm precedence. Male E. hageni have ample opportunity to benefit from sperm precedence, since at least 10% of the receptive females encountered had already mated once that day, but still contained complete or partial clutches of eggs. Female E. hageni benefit directly from high sperm precedence because it allows them to exchange matings for guarding service by males during oviposition bouts under water.     

Fecundity studies on Acartia tonsa (Copepoda: Calanoida) in standardized culture

Acartia tonsa Dana longevity and egg production data were studied over a 4-year period under standardized culture conditions. Egg-laying patterns and daily rates were evaluated as bioassay tools for measuring the nutritional value of various copepod foods, as well as assessing other aspects of environmental quality. Altogether, 337 females were observed in various aspects of this work. Experiments were performed with newly matured females in loosely covered crystallizing dishes. Fresh water and a standard concentration of algae were supplied daily, and a running daily tally was kept of the eggs produced. The effects of male copepods on egg production were analyzed. Males were either removed after the first eggs were observed or they remained with the female throughout her life span. Daily egg-laying rates of this latter group of females appeared to be more stable, but abnormal embryo development occurred if the males were not removed after fertilization. Likewise, the results of females which were not mated were studied. Life spans were shorter and egg production rates were lower than those of contemporary mated females. Unmated females were subjectively observed to be less active than their mated counterparts. The effects of continuous and temporary starvation on egg-laying were also observed. Under both normal and starved conditions, males appeared to have shorter life spans than either mated or unmated females. During starvation there were no real differences between the life spans or egg productions of mated or unmated females. Non-nutritional particulate matter was evaluated as a food source. It was ingested by the females, but did nothing to prolong the egg-laying period. Finally, the three algal components of the standard ration were evaluated. Females produced equally well with a mixed diet or with Thalassiosira pseudonana (100 m³) or Chroomonas salina (140 m³), the two larger species of this diet, but when Isochrysis galbana (40 m³) was fed, females reacted as if in a starved situation.     

Mating success of male hermit crabs in shell generalist and shell specialist species

Summary The reproductive behavior of two species of diogenid hermit crabs was studied in Hawaii. In the shell generalist, Clibanarius zebra, male reproductive success varied little with size, although the largest males were less successful in obtaining copulations than were medium-large males. Male and female size were positively correlated, in successful pairs, thus larger males had the potential to fertilize more eggs when they were successful in obtaining a copulation. Female fecundity in C. zebra was not affected by species of gastropod shell inhabited once female size was taken into account. Male copulatory success was very strongly influenced by the species of gastropod shell inhabited. Males in Trochus or Nerita shells had greatly reduced reproductive success compared to males in Turbo or Nassarius shells. This result was due both to (1) males in Trochus especially dropping and otherwise poorly handling females during precopulatory behavior and (2) females not responding to precopulatory behavior patterns executed by males in Trochus and Nerita. Transferring males from good to bad shapes of shells and vice versa showed that male success was a function of shell type inhabited and not some correlated feature of the crabs. In the shell specialist, Calcinus seurati, which is found primarily in Nerita shells as an adult, males in Nerita shells were quite successful in obtaining copulations.     

Reproduction of the Antarctic fish Nototheniops nudifrons

The reproductive biology of the Antarctic fish Nototheniops nudifrons (Lönnberg, 1905) was analyzed by examination of the gonads of fish collected in March and April 1985 in trawls near Low Island, Antarctic Peninsula, and compared to direct observations of reproduction and early larval development in the laboratory from March to October of the same year. Males and females reached sexual maturity at an age of 4 to 5 yr. Mature males differed in coloration from females and immature males. Ovaries of sexually mature females contained two distinct size modes of vitellogenic oocytes, representing two separate clutches of developing eggs. Females spawned 100 to 3 500 demersal eggs, which were laid in a nest in crevices or under rocks, and guarded by the male for about 4 mo. Females did not assist in nest defense or egg care. Most spawning in the field and in the laboratory occurred in late fall and early winter (May to June). A second clutch may be spawned in spring (November and December). Eggs hatched after 124 d, and larvae were raised for 38 d. Otoliths of larvae contain internal microincrements, which are deposited in a daily fashion, and are visible by light microscopy. The otoliths of 32 adult fish were examined by scanning electron microscope, and counts of microincrements in these otoliths allowed the backcalculation of hatching dates. Estimated hatching dates were between September and May.     

Biologie d'un copépode des mares temporaires du littoral méditerranéen français: Eurytemora velox

The reproduction of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, was studied in winter and spring 1978, under various temperature and salinity conditions, using Chlorella sp. and Amphidinium sp. as food. Maximum numbers of successive eggs sacs (9), eggs per sac (39.3) and total egg production per female (311) were recorded for the witner generation, only 4.8, 34.8 and 109, respectively, for the spring generation. In contrast, the number of eggs per female per day was highest (11.3) in the spring generation, which displayed a more rapid reproductive cycle. Despite strong individual variations in the rhythm of egg sac production and in abundance of eggs per sac, egg production was generally higher during the first third of adult life, attaining a maximum after production of the second or the third egg sac. The continuous presence of the males was necessary to assure complete fertilization of eggs throughout the whole life of adult females. Hatching rate displayed high individual variability, in particular for the spring generation, which had lower average hatching rates (between 0 and 26%, depending on salinity or temperature) than the winter generation (14 to 64%). These differences may be related to the ability of E. velox to produce resting eggs during spring, allowing the species to maintain itself in a temporary water milieu. Temperature significantly affected longevity and daily egg production of females; presence or absence of males did not affect these parameters. An increase in salinity from 20 to 30%. reduced longevity, number of egg sacs, and daily egg production in the winter generation, but not in the spring generation. The specific daily production of females during their adult life was calculated from the egg production:biomass ratio of females, in carbon units. In the winter generation, this ratio increased between 10° and 15°C compared to ratios between 15° and 20°C; the opposite was observed for the spring generation. The seasonal differences in the effects of temperature and salinity on reproduction could indicate an adaptation mechanism to the strongly thermal and haline seasonal fluctuations which characterize the habitat of Ex. velox (brackish waters, drying-up in summer). Larval mortality was high, except at 20%. S for the spring generation. The sex-ratio of the offspring was unaffected by variations in breeding conditions. Hatching time and development time of larvae could be described by two Blehrádek equations displaying close b and () coefficients. We calculated the energy balance of adult females from data obtained in a previous study on feeding and respiration in E. velox, and this is discussed in context with the egg production results. Net growth efficiency varied with algal concentration according to an asymptotic curve, reaching a maximum of 0.43 with Tetraselmis maculata as food or 0.53 with Amphidinium sp. Actual egg production rate obtained in the present study was in good agreement with that calculated by the difference between assimilated food and respiration expenses.     

Underwater oviposition in a damselfly (Odonata: Coenagrionidae) favors male vigilance,and multiple mating by females

Summary Female Enallagma hageni oviposit underwater where they are inaccessible to males. I demonstrate that males guard submerged females rather than perch sites, and are behaviorally distinct from lone males at the water. In contrast to lone males, which always attempt to copulate with females presented to them, guarding males exhibit a conditional latency to remating which corresponds closely to the time required by females to oviposit a complete clutch of eggs. By ovipositing underwater, females decrease the risk that their eggs become exposed. Risks associated with submerged oviposition favor both mate guarding, and multiple, within-clutch matings by females. Both guarding mates and lone males rescue females that float on the water surface as the result of improper resurfacing. Such behavior reduces the mortality risk to females from 0.06 to 0.02 per oviposition bout. By remating between bouts, females benefit from the additional vigilance of lone males, who rescue floating females 1.4 times as often as original mates. A second consequence of multiple mating is an increase in the selective advantage of vigilance by mates. Because receptive females become scarce by early afternoon, whereas male density remains high, a male has little (3%) chance of encountering a second receptive female that day. However, he incurs a 42% risk of losing fertilizations if he abandons a mate. For male E. hageni mate guarding functions in the context of both natural and sexual selection. It insures that a mate lives to lay a complete egg clutch in addition to protecting a male's sperm investment.     

Divide or broadcast: Interrelation of asexual and sexual reproduction in a population of the fissiparous hermaphroditic seastar Nepanthia belcheri (Asteroidea: Asterinidae)

Asexual and sexual reproduction were studied in an intertidal population of Nepanthia belcheri (Perrier) at Townsville, Queensland, Australia, by regular sampling over a year (March 1976-March 1977) and by histological analysis of gonads. Fission reached a peak in early winter (April–June), when about 45% of the population showed evidence of recent fission. Propensity for fission was unrelated to longest arm length. Seven-armed seastars predominated in the population and these underwent fission in two stages to produce one 3-armed fragment and two 2-armed fragments. Fission planes were not related to numbers or positions of madreporites. Hermaphroditism was a normal sexual condition in the population. Almost all gonads contained oocytes, but some gonads functioned as ovaries (without spermatogenic tissue) while others functioned as testes. Seastars with mature ovaries were significantly larger than those with mature testes, indicating protandry, as in other hermaphroditic asteroids. However, fission complicates the pattern of gonad development by causing regression or retardation of gonads and by apparently having a masculinizing effect, so that ovaries may change to testes in fission products. There was a period of sexual reproduction in early summer (October–November). This followed the period of intense fission and regeneration, and a population change from predominately functional females to males. Consequently there was an extreme imbalance against mature females at sexual reproduction, further reducing potential fecundity. Thus, sexual reproduction was very subordinate to fission as the means of recruitment. The 450 m diam eggs probably give rise to pelagic lecithotrophic development and, if this is the case, N. belcheri retains the advantage of complementing reliable recruitment from fission with a dispersive phase. The combination of fission and hermaphroditism is particularly advantageous for a very sparse dispersal of larvae, as a functionally dioecious population may develop from one larva settling in a new locality.     

Development of the pericalymma larva of Solemya reidi (Bivalvia: Cryptodonta: Solemyidae) as revealed by light and electron microscopy

Solemya reidi Bernard 1980 is a gutless protobranch bivalve known to possess intracellular chemoautotrophic bacterial symbionts in its gill. A light and electron microscope study on the embryology and larval development of S. reidi provides data for the bivalve Subclass Cryptodonta. S. reidi spontaneously spawned large eggs (271 m in diameter), which developed within individual gelatious egg capsules. The first several cleavages were equal and a distinct molluscan cross was formed at the animal pole of the embryo, features previously unreported in bivalve development. Lecithotrophic pericalymma larvae (similar to the larvae of paleotaxodont protobranch bivalves and aplacophoran molluscs) hatched at 18 to 24 h and remained in the water column for a further 5 d at 10°C. At hatching, larvae measured from 360 to 440 m in length and from 225 to 265 m in cross-sectional diameter. Definitive adult structures developed within an epithelial locomotory test entirely covered with compound cilia. The test histolysed at metamorphosis and was ingested throught the mouth into the perivisceral cavity. Length and height of the shell following metamorphosis was 433 m (±42 m, n=16) and 282 m (± 29 m, n=13), respectively. Primary data and data from the literature show that the type of larval development in both paleotaxodont and cryptodont bivalves cannot be reliably estimated from egg or prodissoconch sizes.     

Polyandry and its effect on female reproduction in the green-veined white butterfly (Pieris napi L.)

Summary In many insects nutrients transferred by the male to the female at mating are later incorporated into both the eggs and soma of the mated females. Accordingly, it has been suggested that female insects can use these male-derived nutrients both for somatic maintenance and to increase both the number and quality of their offspring. Moreover, much discussion is presently devoted to whether the male nuptial gift represents paternal investment, defined as any increase in given male's total surviving progeny by increasing the reproductive output by a given female, or mating effort which obtains if a male gains by increasing the proportion of eggs he fertilizes from a given female (Parker and Simmons 1989). If the male nuptial gift represents parental investment it should be expected to benefit predominantly the offspring sired by the donor, whereas the physiological fate of the male nuptial gift is somewhat irrelevant under the mating effort explanation. In this paper we test these issues by studying the lifetime fecundity, egg weights and longevity of two groups of females of the polyandrous green-veined white butterfly, Pieris napi, one group of which was allowed to mate only once and the other of which was allowed to mate at liberty, the latter group of females mating on average 2.28 times. Moreover, to test the incorporation rate of male-derived nutrients, we performed a second set of experiments where females were allowed to mate with radioactively labelled males. The results showed that polyandrous females had higher lifetime fecundity compared to monandrous females, laying on average 1.61 as many eggs, and that the difference in cumulative fecundity between the two groups was statistically significant from the 5th day of egg-laying onwards. Polyandrous females also lived longer and maintained egg weight at a high level for longer than monandrous females. Largely concomitant with egg-laying rate, incorporation rate of male-derived nutrients peaked 3–4 days after mating, subsequently tapering off to stabilize at about 40% of the maximum. Given the opportunity, female P. napi remated after 3–5 days, the duration of the refractory period being positively correlated with ejaculate mass. Hence, although the nutrient investment of the first male to mate with a female subsidizes the progeny of later-mating males, the male nuptial gift in P. napi clearly qualifies as both paternal investment and mating effort. Correspondence to: C. Wiklund     

Seasonal observations on the biometry and development in Copepodite Stage V of Calanus finmarchicus from the Firth of Clyde

Relationships between linear dimensions of casts produced at the final moult in the laboratory and definitive sex confirm that Calanus finmarchicus (Gunn.) is sexually dimorphic in Copepodite Stage V. Two forms of Stage V copepodite were present at all times of the year in the Firth of Clyde, Scotland. Except in early spring, when size was similar, these were consistently distinguished by the prosome length. The small form moulted to adult females and the large form to adults of either sex. Relative to the metasome, the length of the cephalosome was greater in the large than small form of Stage V copepodite. This, to an increased extent, distinguished males from all females in the adult. Differences between females of the large and those of the small form were similar in the Stage V copepodite and adult. Feminization in the large form entailed an arrest in the differentiation of secondary male sex-characters. Most morphological females moulting from both forms of Stage V copepodite possessed an apparently normal ovary, with eggs extending into oviducal diverticula. In the case of the large form, however, eggs were occasionally absent from diverticula. The gonad in two specimens resembled an immature testis. In males, a normal testis was always present. Differentiation into the adult male entailed the internal suppression of feminizing factors. On average, within collections, females of the large form moulted later than the small form and definitive males. A similarly consistent difference between females of the small form and males was absent. Moulting times in the large form of Stage V copepodite depended on the presence or not of feminization. Differentiation into the adult male required the environmental stimulation of development. Comparisons with moulting patterns in the sea suggest a mechanism that regulates the recruitment of males to the adult.     

A reliable indicator of female fecundity: the case of the yellow belly in<Emphasis Type="Italic"> Knipowitschia panizzae</Emphasis> (Teleostei: Gobiidae)

A large body of research has developed on male ornaments and their role in sexual selection while female ornaments have been less investigated. This study focused on the presence, function, and possible role of a sexually dimorphic nuptial trait as an indicator of female quality in a fish species presenting conventional sex roles: the yellow patch on the belly of Knipowitschia panizzae females. Aquarium spawning experiments demonstrated that this ornament is due to dermal pigments, is displayed only when the female is ready to spawn, and is switched off within minutes from the end of egg deposition. This sexual trait is variable in size among females and indicates female fecundity relative to her own body size. As a consequence, female yellow belly appears to be a reliable indicator of female quality as measured by current fecundity. Field data on natural nests highlights that males usually perform parental care on only one egg batch at a time. The modality of egg deposition suggests that males may be limited in their potential reproductive rates by environmental factors. Male limitations in egg care could favour male choosiness and the evolution of female nuptial displays.Communicated by R. Cattaneo-Vietti, Genova     

Selective males and ardent females in pipefishes

Summary In the pipefishes Syngnathus typhle and Nerophis ophidion, males have been shown to limit female reproductive rate, and females to compete for access to males. Hence, these species fit the criteria for sex-role reversal. Males brood the eggs and provide the offspring with nutrients, oxygen and an osmoregulated environment. Moreover, in S. typhle both sexes prefer a larger mate when given a choice. Sexual selection theory predicts that males should be more choosy than females, and that was experimentally demonstrated in this study. We predicted that S. typhle males should be less eager to copulate than S. typhle females with an unattractive (i.e. small) mate. We measured eagerness as the time from the start of the experiment until copulation occurred. Males with unattractive partners took significantly longer to copulate than females with unattractive partners. Moreover, females invariably initiated the courtship dance, and resumed it quicker after copulation than did the males, again suggesting reproductive hesitation in males. Neither male nor female size per se was correlated with time until copulation. In N. ophidion, where we have previously shown that males prefer larger to smaller females, we found that females did not select males with regard to size. Our results are consistent both with earlier findings (males limit female reproduction and females compete for males) and with operational sex ratios in nature: in seven annual field samples in June, the numbers of S. typhle females with ripe eggs always significantly exceeded numbers of receptive males. Hence, the potential cost of being choosy in terms of lost matings is much higher in females than in males. In conclusion, S. typhle females were somewhat choosy, but less so than males, whereas N. ophidion females were not choosy at all. Correspondence to: A. Berglund     

The pursuit of extra-pair copulations by monogamous female razorbills: how do females benefit?

Summary Monogamous female razorbills Alca torda actively sought extra-pair copulations (EPCs) in mating arenas outside their nesting colony. Females showed marked variation in promiscuity, defined as the number of EPCs they accepted (0–7), and in receptivity, defined as the percentage of EPC opportunities accepted (0%–100%). The opportunity of females to encounter males for EPCs was measured by (a) the time spent in the mating arena, and (b) the guarding effectiveness of their mates. Females appeared to encounter males and accept EPCs independently of opportunity, which suggests that variation in promiscuity and receptivity is caused by differences in the degree to which individual females might benefit from EPCs. I tested predictions of four hypotheses which propose benefits which females could obtain from EPCs: good genes, genetic diversity of offspring, insurance against infertility of mate, and acquisition of a new mate. No evidence was found to support two predictions made exclusively by the good genes hypothesis: (a) paired males did not achieve greater EPC success than unpaired males, and (b) males who were cuckolded did not obtain fewer EPCs than males whose mates avoided EPCs, suggesting that a male's attractiveness to other females does not ensure his own mate's fidelity. A prediction of both the insurance and good genes hypotheses was supported: females (who in this species retain their mates between years) showed similar receptivity to EPCs between years. This finding contradicts the genetic diversity hypothesis which predicts that in species that lay one egg per year, females who refuse EPCs in one year will accept them in the next. The good genes and genetic diversity hypotheses both predict that females who accept EPCs will behave as if to maximize their chances of being fertilized by extra-pair males. Results contradicted this prediction: females who accepted EPCs were more, rather than less receptive to their mates' copulation attempts than were females who did not accept EPCs. This finding is compatible with the insurance hypothesis which only requires females to store the sperm of extra-pair males, without necessarily being fertilized by it. Insurance against male infertility was the only hypothesis whose predictions were not contradicted by any of the results.