Ecology of a corallivorous gastropod,<Emphasis Type="Italic"> Coralliophila abbreviata</Emphasis>, on two scleractinian hosts. I: Population structure of snails and corals

Despite their potential importance in structuring reef communities, invertebrate corallivores and their population structures are poorly understood. We found distinct differences in the population structures (length-frequency distribution and sex ratio) of the corallivorous gastropod Coralliophila abbreviata residing on two coral-host taxa, Montastraea spp. and Acropora palmata, in the Florida Keys. In each of two survey years, around 50% of the Montastraea spp. colonies were infested, with a mean snail density of eight snails per infested colony (range 1–45), while around 20% of A. palmata colonies harbored three snails per infested colony (range 1–23). Variation in patterns of snail occurrence was also observed within a host taxon. A. palmata occurred in low- and high-density stands (0.4 and 1 colony m^–2, respectively, at the initial survey) at different sites. Hurricane Georges struck the area in September 1998. When resurveyed in 1999, density of colonies in low-density stands had decreased by 75% to 0.1 colonies m^–2. This decrease was accompanied by a doubling in the proportion of colonies infested with snails (from 19% to 46%) and an increase in snail density per infested colony (from 3.7±3.3 SD to 5.4±4.6 SD) as snails apparently concentrated on surviving A. palmata. In contrast, sites with high density A. palmata stands (thickets) retained colony densities of about ~1 colony m^–2 among years, while snail infestation increased only from 9% to 14% of colonies surveyed and snail density essentially remained unchanged (from 2.7±1.8 to 2.9±1.9 snails per infested colony). Snails collected from Montastraea spp. were shorter than those from A. palmata in low-density stands and were longest on A. palmata in thickets. On both host taxa, female snails were longer than males. The sex ratio of snails on Montastraea spp. hosts was even (1:1), while that of snails on A. palmata was skewed (70% males). Factors that could explain observed differences in size structure and sex ratio between Coralliophila populations on the two coral host taxa include: differential susceptibility to predators, influence of host tissue nutritional quality and/or secondary metabolite content, and genetic differences (cryptic species). The host-specific characteristics of C. abbreviata populations imply that the impact of gastropods on reef communities will vary with the coral species composition.     

Male-male competition selects for delayed sex change in the protandrous shrimp<Emphasis Type="Italic"> Pandalus latirostris</Emphasis>

In most protandrous species, male size advantage is generally regarded as unimportant in determining the timing of protandrous sex change. In pandalid shrimp, the size/age of male sex change often fluctuates among years and populations, but the adaptive significance of late reversing males (LRMs) is not well understood. This study experimentally examined the adaptive significance of LRMs in the protandrous pandalid shrimp Pandalus latirostris Rathbun. Field and laboratory studies were carried out in August–September of 1998–2002 on P. latirostris in Notoro Lagoon, Japan (44°03′N; 144°10′E). Mature females that had molted (i.e. mate receptive) were tethered in the field and their mating behavior with wild males was observed. Copulations occurred with a single male at a time, although other males could sequentially mate with a tethered female. Because tethered females rejected male approaches, males had difficulty transferring their spermatophores. In the laboratory, males copulated with non-tethered, recently molted females for only 15 min after molting. Recently molted females are wary of potential predators, since their soft exoskeleton makes them particularly vulnerable. Fast access by males enhanced fertilization success in this shrimp. The effect of male size on mating success in the laboratory was examined. Both small and large males successfully inseminated females in the absence of competitors. In experiments where large, medium, and small males competed for a female, however, larger males guarded females longer than smaller males, until the female molted and became receptive. Moreover, large males were more successful at copulating once molting occurred. These results imply that male-male competition drives delayed sex change in some situations.     

Population structure and sex-change in the coral-inhabiting snailCoralliophila violacea at Hsiao-Liuchiu,Taiwan

Surveys of the coral-inhabiting snailCoralliophila violacea (Lamarck) (=C. neritoidea Kiener) were made on shallow fringing reefs (<8 m deep) around Hsiao-Liuchiu, Taiwan, between July and October 1990. The snails were aggregated into patches on the surface of massive poritid coral colonies. Coral colonies >40 cm in diameter were more likely to bear patches of snails than smaller colonies, and also to have more snails. The coralliophilids ranged from 5 to 30 mm in aperture length. The sex ratio of the population was biased toward males (539:279), with only a few small individuals of indistinguishable sex. Snails between 6 and 10 mm were all males, while most snails with aperture lengths 20 mm were females. Judging from the distinct size ranges of males and females within patches and from the observed degeneration of the penis, the snails may have changed sex from male to female with increasing size. Sex-change may occur across a wide size range (10 to 20 mm). The correlation of smallest female size and largest male size among patches indicates that snail size at sex-change is peculiar to each individual patch. Those females in patches with a single female (but many males) were significantly smaller than females in multiple-female patches. It is likely that in the absence of females males change sex at a smaller size, whereas in the presence of large females males delay sexchange until they have reached a larger size. The plasticity of size at sex-change may be adaptive and a result of natural selection at the individual level.     

Effects of season and maternal food on<Emphasis Type="Italic"> Calanus finmarchicus</Emphasis> reproduction,with emphasis on free amino acids

Effects of maternal food environment and season were examined during spring and autumn on females, eggs and nauplii of Calanus finmarchicus, in different natural prey suspensions or cultures of Rhodomonas baltica. Females sampled in spring were in general larger, had higher protein content, and showed higher egg production and hatching rates, than in autumn. The cumulative egg production was almost double in spring compared to autumn (females fed R. baltica). Females had higher content of free amino acids (FAA) and free essential amino acids (EAA) in autumn than in the spring. Also, the FAA contents in eggs and nauplii were higher in autumn than in spring. In contrast, the composition of EAA in eggs was constant between seasons, indicating maternal regulation. The highest cumulative egg production was correlated with a high similarity in the free pool of EAA in the food suspension and the female copepod. Thus, the data support the hypothesis that similarity in the free pool of EAA of diet and female promotes high fecundity and egg hatching success in C. finmarchicus.     

Lack of innate preference for morph and species identity in mate-searching <Emphasis Type="Italic">Enallagma</Emphasis> damselflies

Insect mate recognition is often viewed as stereotypic, innate, and species-specific. However, male damselflies can learn to identify female-specific color morphs as potential mates. A suite of male mimicry hypotheses assume that heteromorphic females, which differ from males in color pattern, are more easily recognized as “female” and thus lack the inherent, anti-harassment advantage that the more male-like signal provides for andromorphs. Using two measures of male preference, we investigated whether naïve males have a preexisting sensory bias for a given morph color in Enallagma civile, a species that appeared to exhibit extreme plasticity in morph expression across generations within a breeding season. E. civile males raised in the absence of females exhibited no preference for either morph, whereas males raised with one female type exhibited a learned sensory bias for that morph. Male Enallagma also lacked a bias toward conspecific females over a congeneric sister species. In a naturally naïve population of Enallagma ebrium, males reacted sexually to both morphs of Enallagma hageni as often as they did to conspecific females, whose thoracic spectra were nearly identical with those of E. hageni. Moreover, despite the similar thoracic spectra of males and andromorphs, both of which reflected UV, males rarely reacted sexually to other males. Our results falsified implicit assumptions of male mimicry hypotheses, supported learned mate recognition, and suggested a scenario for speciation via sexual conflict.     

Call structure may affect male mating success in the quacking frog<Emphasis Type="Italic"> Crinia georgiana</Emphasis> (Anura: Myobatrachidae)

We investigated the relationship between mating success, male size and variation in the advertisement call in the frog Crinia georgiana under field conditions. Mating success in 91 males was determined by following 32 females as they moved through the chorus. Our analyses indicated that successful males had a higher number of pulses in the first note and/or called at a higher rate. However, we did not detect a significant relationship between mating success and dominant frequency, the property that varied most strongly with body size, suggesting that size is not an important influence on mate choice in this species. Even so, smaller males were more successful if they called at a higher rate whereas larger males were more successful if they had more pulses in their first note. Accordingly, males of different size may use different calling tactics to attract females. These results provide a framework for further experimental studies aimed at investigating the independent impacts of both inter- and intra-sexual selection on the advertisement call and body size of C. georgiana.     

Forced dispersal of juvenile guanacos (<Emphasis Type="Italic">Lama guanicoe</Emphasis>): causes,variation, and fates of individuals dispersing at different times

We examined adult-juvenile conflict in the guanaco (Lama guanicoe). During spring, territorial males become increasingly aggressive toward all juveniles born the previous year and begin expelling them from family groups. In an apparent effort to reduce aggression, juveniles display submissive crouches when being observed, approached, or attacked by the territorial male. Therefore, we assessed the influence of juvenile submissive behavior on the timing of dispersal and also examined if dispersal time was related to survival and reproductive performance as adults. We also evaluated hypotheses regarding the evolution of juvenile mammalian dispersal in the context of if and how each may favor the forced dispersal of juvenile guanacos by territorial males. Juveniles generally dispersed in late spring and early summer, and a nearly equal proportion of females (n=46; 48%) and males (n=49; 52%) dispersed. More-submissive animals generally dispersed later than less-submissive animals. Juvenile sex and dispersal time were not related to survival. In contrast, juvenile sex and dispersal time were related to reproductive performance. The probability of reproducing was highest when juveniles dispersed early and decreased with increasing time in family groups prior to dispersal. The largest proportion of juveniles was forced to disperse during a 2-week interval following the peak of the breeding season. Competition for food resources is likely very intense at this juncture and territorial males may force older juveniles to disperse in order to divert food resources to younger neonates. Additionally, juveniles may be forced to disperse after territorial males mate their mothers to prevent lost mating opportunities, because females leave territories when their offspring disperse and possibly prior to mating with males. We conclude that the forced dispersal of juvenile guanacos by territorial males is ultimately driven by competition for food resources on territories. The timing of dispersal, however, may be tempered by the chronology of matings between territorial males and particular adult females, and/or genetic relatedness between territorial males and juveniles.     

Male-biased sex ratios in New Zealand fur seal pups relative to environmental variation

A number of models have been proposed to provide adaptive explanations of sex-ratio variation in mammals. Two models have been applied commonly to primates and ungulates with varying success—the Trivers-Willard (TW) hypothesis, and the local resource competition (LRC) hypothesis. For polygynous, sexually dimorphic mammals, where males are larger and disperse more readily, these models predict opposite outcomes of sex-ratio adjustment within the same environmental context (high-resource years: TW—more sons; LRC—more daughters). However, many of the predictions of these two models can vary depending on factors influencing resource availability, such as environmental stochasticity, resource predictability, and population density. The New Zealand fur seal (Arctocephalus forsteri) is a polygynous mammal showing marked sexual dimorphism (larger males), with higher variation in male reproductive success expected. We provide clear evidence of male-biased sex ratios from a large sample of A. forsteri pups captured around South Island, New Zealand during 1996/1998, even after accounting for a sex bias in capture probability. The extent of the bias depended upon year and, in 1998, strong climatic perturbations (El Niño/Southern Oscillation, ENSO) probably reduced food availability. Significant male-biased sex ratios were found in all years; however, there was a significant decline in the male bias in 1998. There was no relationship between sex ratio and population density. We suggest that the sex-ratio bias resulted from the production of relatively more male pups. Under the density-independent scenario, the strong male bias in A. forsteri sex ratios is support for the TW model within an environment of high resource predictability. We suggest that some plasticity in the determination of pup sex among years is a mechanism by which A. forsteri females in New Zealand, and perhaps other otariid seals, can maximise fitness benefits when living in regions of high, yet apparently predictable, environmental variability. We also suggest that much of the inconsistency in the reported sex ratios for otariid seals results from the complex interaction of population density and environmental stochasticity influencing relative food availability over time.     

Intraspecific brood parasitism as a conditional reproductive tactic in the treehopper<Emphasis Type="Italic"> Publilia concava</Emphasis>

In species exhibiting egg guarding as well as communal egg laying, females may adopt the strategy of laying eggs in the nests of conspecifics and leaving without providing care (termed intraspecific brood parasitism). This study is the first to describe such a behavior in the insect Publilia concava (Hemiptera: Membracidae) through field studies that followed 849 marked females across 1,828 brood associations. While brood parasitism increased the total number of eggs in a host brood, it did not reduce the overall hatching success of host broods. Solitary females exhibited a range of guarding durations while parasitic females rarely remained to guard eggs. Females exhibiting the parasitic tactic increased their lifetime number of clutches without decreasing the number of solitary clutches that they were able to initiate. Estimates of egg number for these individual broods revealed that females adopting the parasitic tactic (in addition to solitary breeding) had higher lifetime fecundity relative to females that did not parasitize. In females that exhibited both tactics (solitary and parasitic), the parasitic tactic yielded a higher rate of oviposition. The major component of oviposition rate was the time to find hosts and this time decreased with increasing host availability across 222 replicate groups. Females exhibited a shift toward the parasitic tactic when host broods were more abundant (i.e. in larger groups and later in the season). However, the time to find hosts increased as the frequency of the parasitic tactic increased, suggesting that this tactic may be maintained through negative frequency dependence. The results of this study suggest that brood parasitism may be the preferred tactic, as part of a conditional strategy, when hosts are readily available with solitary breeding being the preferred tactic when hosts are in short supply.     

Offspring sex ratio variation in the bridled nailtail wallaby, Onychogalea fraenata

The bridled nailtail wallaby is a sexually size dimorphic, promiscuous, solitary macropod. Sex ratios of pouch young were studied at two sites over 3 years, beginning with 14 months of severe drought. Females that were in better condition were more likely to have sons, and condition was dependent on body size. Females at one site were heavier, were consequently in better condition, and produced more sons than females at the other site. Females that declined in condition had more daughters during the most severe part of the drought than females that maintained condition, but endoparasite infection did not affect the pouch young sex ratio. Age also appeared to affect sex ratio adjustment, because weight was strongly influenced by age. Sex ratio bias was not caused by early offspring mortality, but occurred at conception. Mothers did not appear to bias energy expenditure on sons or daughters; males and females did not differ in condition at the end of pouch life. Pouch young sex ratio variation was most consistent with the Trivers-Willard hypothesis, but could also have been influenced by local resource competition, since sons dispersed further than daughters. Offspring condition was related to survival, and was correlated with maternal condition. Received: 14 April 1998 / Accepted after revision: 10 November 1998     

Reproduction of<Emphasis Type="Italic"> Ophiactis resiliens</Emphasis> (Echinodermata: Ophiuroidea) in New South Wales with observations on recruitment

Reproduction of the ophiuroid Ophiactis resiliens Lyman 1879, a common species in the shallow waters around Australia, was examined over 1 year in two populations near Sydney, New South Wales. Gametogenesis was documented by histological examination of the gonads. Vitellogenesis in females and spermatocyte proliferation in males started in February and March. O. resiliens had an annual spawning period from May to September/October with peak gamete release from May to July. Thereafter, spawning occurred in some specimens through November. Gravid gonads were present for approximately 2 months longer in O. resiliens from Clovelly Bay than in those from Little Bay. At both sites spawning was episodic and gametogenesis continued through most of the spawning season. Most specimens (50–100%) collected from November to March had indeterminate/recovery stage gonads, the sex of which, could not be determined. The timing of gametogenic renewal during these months varied among individuals. O. resiliens has a 3-month planktonic stage and the presence of juveniles, 0.5 –1.5 mm disk diameter, in the coralline algal turf at Little Bay from February to May, suggests that settlement occurs in summer and autumn at this site. In contrast, juveniles were rarely encountered in coralline turf at Clovelly.     

Local mate competition in the solitary parasitoid wasp <Emphasis Type="Italic">Ooencyrtus kuvanae</Emphasis>

Local mate competition (LMC) occurs when brothers compete with each other for mating opportunities, resulting in selection for a female-biased sex ratio within local groups. If multiple females oviposit in the same patch, their sons compete for mating opportunities with non-brothers. Females, in the presence of other females, should thus produce relatively more sons. Sex ratio theory also predicts a more female-biased sex ratio when ovipositing females are genetically related, and sex-ratio responses to foundress size if it differentially affects fitness gains from sons versus daughters. The mating system of the parasitoid wasp Ooencyrtus kuvanae meets assumptions of LMC. Females insert a single egg into each accessible egg of gypsy moth, Lymantria dispar, host egg masses. Wasps complete development inside host eggs and emerge en masse, as sexually mature adults, resulting in intense competition among brothers. We tested the hypothesis that O. kuvanae exhibits LMC by manipulating the number of wasp foundresses on egg masses with identical numbers of eggs. As predicted by LMC theory, with increasing numbers of wasp foundresses on an egg mass, the proportions of emerging sons increased. In contrast, the presence of a sibling compared to a non-sibling female during oviposition, or the size of a female, did not affect the number or sex ratio of offspring produced. The O. kuvanae system differs from others in that larvae do not compete for local resources and thus do not distort the sex ratio in favor of sons. With no resource competition among O. kuvanae larvae, the sex ratio of emergent son and daughter wasps is due entirely to the sex allocation by ovipositing wasp foundresses on host egg masses.     

Why do female mice mate with multiple males?

Females often show multi-male mating (MMM), but the adaptive functions are unclear. We tested whether female house mice (Mus musculus musculus) show MMM when they can choose their mates without male coercion. We released 32 females into separate enclosures where they could choose to mate with two neighboring males that were restricted to their own territories. We also tested whether females increase MMM when the available males appeared unable to exclude intruders from their territories. To manipulate territorial intrusion, we introduced scent-marked tiles from the neighboring males into males' territories, or we rearranged tiles within males' own territories as a control. Each female was tested in treatment and control conditions and we conducted paternity analyses on the 57 litters produced. We found that 46 % of litters were multiply sired, indicating that multiple paternity is common when females can choose their mates. Intrusion did not increase multiple paternity, though multiple paternity was significantly greater in the first trial when the males were virgins compared to the second trial. Since virgin male mice are highly infanticidal, this finding is consistent with the infanticide avoidance hypothesis. We also found that multiple paternity was higher when competing males showed small differences in their amount of scent marking, suggesting that females reduce MMM when they can detect differences in males' quality. Finally, multiple paternity was associated with increased litter size but only in the intrusion treatment, which suggests that the effect of multiple paternity on offspring number is dependent on male–male interactions.     

Variation in fertilisation abilities between hemiclonal hybrid and sexual parental males of sympatric water frogs (<Emphasis Type="Italic">Rana lessonae</Emphasis>,<Emphasis Type="Italic"> R. esculenta</Emphasis>,<Emphasis Type="Italic"> R. ridibunda</Emphasis>)

In many species, males and females mate with multiple partners, which gives rise to sperm competition and multiple paternity. The experiments on water frogs presented here demonstrate that such sperm competition can affect the structure and dynamics of mixed-species communities. The hybrid frog Rana esculenta (LR) mates with one of its parental species, usually R. lessonae (LL), although in some areas R. ridibunda (RR), to regain the premeiotically eliminated parental genome ("hybridogenesis"). Mixed LL/LR-populations are stable although hybrid numbers should continuously increase at the expense of parental animals, because of differences in female fecundity and other factors. This would finally lead to the extinction of the sexual host, followed by that of the sexual parasite, unless the reproductive superiority of R. esculenta is reduced by other factors, such as lower hybrid male fertility. Eggs from LL- and LR-females were fertilised in vitro by single- and multi-male sperm suspensions of LL-, LR- and RR-males. In all experiments, the proportion of offspring sired by R. esculenta sperm was significantly lower than that sired by R. lessonae or R. ridibunda sperm. Gonad mass, sperm morphology, sperm swimming velocity, and sperm survival did not explain these differences in fertilisation success; nor did gamete recognition and compatibility. Sperm density was the only trait that paralleled fertilisation success, but it offers no explanation either, because densities were equalised for the in-vitro fertilisations. In natural LL/LR populations, the significantly smaller amount, poorer competitive ability and lower long-term survival of R. esculenta compared to R. lessonae sperm will reduce the initial reproductive superiority of hybrids and contribute to the stabilisation of mixed water-frog populations. Differences in fertilisation ability are also likely to be relevant for the structure and dynamics of several other systems with encounters between eggs and sperm from different genotypes, ecotypes, ploidy levels and/or species.     

Geographical expansion of the invader <Emphasis Type="Italic">Caprella scaura</Emphasis> (Crustacea: Amphipoda: Caprellidae) to the East Atlantic coast

Caprella scaura (Templeton in Trans Entomol Soc Lond 1:185–198, 1836) is a native species to the western Indian Ocean. It was first described from Mauritius and later reported from several regions of the world. During the last decade, the species spread out of the Adriatic Sea, and in 2005, C. scaura was reported in Gerona, on the north-eastern coast of Spain. The present study shows the recent rapid expansion of the species to the East Atlantic. During a sampling survey of harbours along the Strait of Gibraltar (Dec 2009–June 2010), we found high densities of C. scaura associated with the bryozoans Zoobotryon verticillatum Della Chiaje, 1822, in Chipiona and Bugula neritina (L.) in Cádiz, Atlantic coast of southern Spain; on the other hand, during May 2009, an important population of C. scaura was also found in the Canary Islands (Tenerife) associated with aquaculture resources. A total of 1,034 individuals of C. scaura were studied, and we confirm that the populations are effectively established, with high densities and reproducing females during the whole year. The population from Cádiz was characterised by smaller specimens but a higher number of eggs per female. These differences could be related to environmental conditions, mainly sea water temperature and to other factors such as competition with other species, or availability of food or substrate. Significant correlation was found between female size and number of eggs in the three populations, but egg size did not vary with female body length. The morphometric relation length/width of the second gnathopod was also calculated and compared between sexes: larger males presented longer gnathopods at the three sites. The most probable introduction vector of this species is shipping; in fact, the Strait of Gibraltar is characterised by an intense shipping traffic. Also, we have observed that the native Caprella equilibra Say, 1818, is being displaced by C. scaura in the harbour of Cádiz, where this species reach densities of 35,945 ind/1,000 g of B. neritina. Further experimental studies are necessary to explore the potential danger of this species, which might spread into natural habitats too.     

Identification of a floral-derived kairomone for currant clearwing, <Emphasis Type="Italic">Synanthedon tipuliformis</Emphasis>

The currant clearwing Synanthedon tipuliformis (Clerck) (Sesiidae) is a worldwide pest of black currants, Ribes nigrum. This moth has been observed to feed on nectar of inflorescences of Canada thistles, Cirsium arvense (L.) Scop. This work was undertaken to identify floral compound(s) produced by Canada thistles inflorescences that mediate the response of the currant clearwing. Floral volatiles were collected during the day and analysed by coupled gas chromatography/electroantennographic detection (GC/EAD) and gas chromatography/mass spectrometry (GC/MS). Three compounds consistently elicited EAD response from moth antennae and were identified by GC/MS as phenylacetaldehyde, methyl salicylate and dimethyl salicylate. When the compounds were tested individually or in various combinations in field trapping experiments, a 3-component blend attracted the largest number of female and male currant clearwings. Subsequent field trapping experiments were conducted to determine the optimal attraction dose for the ternary blend using three loadings of 1, 10 and 100 mg loaded into a polyethylene sachet. The highest catches were in traps baited with the 100 mg loading. In all trials, males and mated females were caught in significant numbers, while very low numbers of virgin females were found in the traps. In recent years the efficacy of mating disruption against currant clearwing has been reported as declining. The new kairomone blend identified in this study can be used with the sex pheromone to provide an effective control option for this important pest.     

Variation in size at sex-change among natural populations of the protandrous hermaphrodite, <Emphasis Type="Italic">Crepidula fornicata</Emphasis> (Gastropoda,Calyptraeidae)

Protandrous hermaphrodites are predicted to change sex from male to female when relative reproductive fitness of females surpasses that of males. How size at sex transition varies with population, mating group and individual parameters was investigated for five populations of the protandrous hermaphrodite slipper snail, Crepidula fornicata. The populations varied for density, size distribution, average mating group size and sex ratio. Size at sex-change was correlated with the population sex ratio. Comparisons of multiple hypotheses revealed that variables predicting the sex of a snail vary among positions in the mating group. The variables included body size, the relative size of the snail sitting atop the focal snail and population density. Our data support the conclusions that size at sex-change (and by inference, the size at which one sex has relatively greater fitness) is not fixed for these hermaphrodites and that individual size, social conditions and population differences all influence variation in relative fitness.     

Patterns of gamete incompatibility between the blue mussels<Emphasis Type="Italic"> Mytilus edulis</Emphasis> and<Emphasis Type="Italic"> M</Emphasis>.<Emphasis Type="Italic"> trossulus</Emphasis>

Previous research on gametic incompatibility in marine invertebrates suggests that for highly dispersive marine invertebrate species, barriers to fertilization among closely related taxa are often incomplete and sometimes asymmetric. The nature of these barriers can dramatically affect the patterns of gene flow and genetic differentiation between species, and thus speciation. Blue mussels, in the genus Mytilus, are genetically distinct in allopatry yet hybrids are present wherever any two species within the group co-occur. The present study sampled M. edulis (L.) and M. trossulus (Gould) in May and June 2001 from the East Bay section of Cobscook Bay, Maine, USA (latitude 44°56′30″N; longitude 67°07′50″W), where the two species are sympatric. Gamete incompatibility was investigated in a series of laboratory fertilizations carried out in July 2001. The proportion of fertilized eggs typically exceeded 80% at sperm concentrations of 10³–10⁴ ml^?1 among intraspecific matings (n=18), but was <30% even at sperm concentrations in excess of 10⁵–10⁶ ml^?1 for interspecific matings (n=13). Further analysis indicated that approximately 100- to 700-fold higher sperm concentrations were required to achieve 20% fertilization in interspecific matings relative to intraspecific matings, indicating strong barriers to interspecific fertilization. The proportion of fertilized eggs did not follow this general pattern in all matings, however. The eggs from two (out of five) M. edulis females were almost as receptive to M. trossulus sperm as they were to M. edulis sperm. In contrast, the eggs from all M. trossulus females (n=3) were unreceptive to M. edulis sperm, suggesting that fertilization barriers between these species may be asymmetric. Given the experimental design employed in this study, the results are also consistent with a strong maternal or egg effect on the level of interspecific gamete compatibility in M. edulis.     

Abnormal gonadal morphology in intersex,<Emphasis Type="Italic"> Echinogammarus marinus</Emphasis> (Amphipoda): a possible cause of reduced fecundity?

Recent reports have demonstrated a cost associated with intersexuality in Amphipoda, including reduced fecundity and fertility. In this study, the gross morphology of the gonads in normal and intersex Echinogammarus marinus (Amphipoda) were compared to determine whether resource allocation to gonadal tissue accounted for this reduced fitness. Evidence for the presence of the male sex-determining hormone, androgenic gland hormone (AGH), was compared between sexual phenotypes using MALDI mass spectrometry. Two distinct intersex phenotypes (‘male’ intersex and ‘female’ intersex) were found, with variation in gonadal structure corresponding with external phenotype. Examination of male intersexes revealed normal testicular development (testes, seminal vesicles and vas deferens), but also revealed the formation of an oviduct. Ovaries of intersex females showed normal ovarian development, but were reduced in length by approximately 20% due to the presence of vas deferens. The number of vas deferens in intersex females was equal to the number (one or two) of genital papillae. We hypothesise that the reduced ovarian length observed in intersex females is a likely cause of the reduced brood size previously reported in intersex females of this species. Variation in the sexual phenotype corresponded both to development of the androgenic gland and to expression of a peptide fragment corresponding to the A chain of androgenic gland hormone (AGH). Androgenic glands and a putative AGH peptide were present in males. However, in both normal and intersex females, the androgenic glands were only present in a rudiment form and the peptide was not detected. Intersex males were found to possess abnormal glands that appeared hypertrophied. However, AGH peptides were not detected, supporting the suggestion that the intersex phenotype is manifested via perturbations of AGH.     

Sexual selection and female fitness in <Emphasis Type="Italic">Drosophila simulans</Emphasis>

There is a current debate over the net fitness consequences of sexual selection. Do preferred males increase female fitness or are these males manipulating females for their own benefit? The evidence is mixed. Some studies find that mating with attractive males increases female fitness components, while others show that preferred males decrease measures of female fitness. In this study, we examined some of the fitness consequences of pre-copulatory sexual selection in Drosophila simulans. Virgin females were either paired with one male and given an opportunity for one copulation or were exposed simultaneously to two males. This allowed us to compare female preference (copulation latency) and fitness (longevity, lifetime productivity and rate of offspring production) both with and without the influence of male–male competition. When females had access to a single male, neither female longevity, productivity, nor short-term rate of productivity were associated with female preference, and although females mated more quickly with larger males, male size was also not associated with any female fitness measure. Inclusion of male–male competition showed that female longevity was negatively affected by preference, while productivity and rate of productivity was unaffected. This latter experiment also indicated that females preferred larger males, but again, male size was not associated with female fitness. These results indicate that females may not benefit from mating with preferred males, but they may incur survival costs.