Age and growth of the mesopelagic squid Ancistrocheirus lesueurii (Oegopsida: Ancistrocheiridae) from the central-east Atlantic based on statolith microstructure

Statolith microstructure was studied in 56 Ancistrocheirus lesueurii (25 to 423 mm of mantle length, ML) caught in the central-east Atlantic. Statolith growth increments were grouped into three main growth zones, distinguished mainly by increment width. The second transition in the statolith microstructure (from Zone 2 to Zone 3) coincides with the life history shift from epipelagic and upper mesopelagic to a bathyal habitat. Second-order bands (mean 27.65 growth increments) and sub-bands (mean 13.6 growth increments) within statolith microstructure appeared to be related to the lunar cycle. Striking sexual dimorphism is reflected in the age and growth rates: males live ca. 1 yr, while females only start maturing at this age and obviously live >1.5 yr. A. lesueurii is a slow growing squid, attaining 25 to 30 mm ML at the age of 100 d. After ontogenetic migrations into bathypelagic waters at ML > 30 to 35 mm, growth rates gradually decrease to the minimum known values for squids. Based on back-calculated hatching dates, A. lesueurii hatches throughout the year with a peak between November and March. Received: 28 August 1996 / Accepted: 31 January 1997     

Determinants of mating success in the golden hamster (Mesocricetus auratus) IV. Sperm competition

Summary This study was designed to clarify several aspects of sperm competition in the golden hamster (Mesocricetus auratus). By mating females homozygous for a recessive coat color gene with two males, one homozygous for the dominat gene (agouti) and one homozygous for the recessive (cream), paternity of the resulting young could be determined by day 2 postpartum. When females received 5 consecutive ejaculations from a male of one strain followed by 5 ejaculations from a male of the other strain, there was a significant advantage with respect to litter composition for the male ejaculating first. A mechanism for the first male mating advantage was suggested by the results of an experiment in which the time interval between first and second males was varied. Delays of 30 min between first and second males significantly increased the proportion of young sired by the first male. With a delay of 8 h, the first male sired all of the young. Delays between matings by males of the two strains had greater effects when mating tests began around the time of ovulation, rather than several hours before. Ejaculations in excess of those required for pregnancy initiation were shown to have a two-fold effect. They afforded the first male a measure of protection against displacement by a subsequent male. Conversely, prolonged copulation by the second male resulted in significant displacement of the sperm of a predecessor. The protective effects of multiple ejaculations by the first male were mediated by two mechanisms: the delay in introduction of competing sperm and an increase in the relative concentration of the first male's sperm. Prolonged copulation by the second male also appeared to function through its effect on relative sperm concentrations. Males of these genotypes differed with respect to the relative fertilizing capacity of their cjaculates. When ejaculations from males of the two strains were alternated (thus minimizing mating order effects), agouti males sired over 90% of the young. The time during which mating tests were conducted (relative to the occurrence of ovulation) had no effect on the relative performance of the strains. The effects of prolonged copulation and first male mating advantage demonstrated in this study are consistent with observations of mating behavior under semi-natural conditions. Thus, it appears that patterns of sperm allocation and manipulation, male and female mating strategies, and mating systems have coevolved.     

Sperm parasitism in ants: selection for interspecific mating and hybridization

Interspecific mating in eusocial Hymenoptera can be favored under certain conditions even if all hybrid offspring are completely infertile. This exploits two key features of the eusocial Hymenoptera: a haplodiploid genetic system and reproductive division of labor in females. Interspecifically mated queens can still produce viable sons that will mate intraspecifically. Apparent reduced fitness resulting from producing infertile daughter gynes can be also offset by advantages conferred by hybrid workers. An important advantage is likely to be superior ability at using marginal habitats. Interspecifically mated queens can nest in sites where intraspecific competition will be low. By mating interspecifically, a queen trades expected reproductive success through female offspring for a higher probability of achieving some reproductive success. Females that mate interspecifically can be considered "sperm parasites" on the males of the other species. I provide evidence that sperm parasitism is responsible for widespread hybridization in North America among two species of the ant subgenus Acanthomyops (genus Lasius), and review evidence for sperm parasitism in other hybridization phenomena in ants. Sperm parasitism in ants represents a novel form of social parasitism in ants and a dispersal polymorphism. It may also act as a precursor to the evolution of some other recently discovered phenomena, such as genetic caste determination.     

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.     

Male size,mating success,and mating strategy in the mosquitofish Gambusia affinis (Poeciliidae)

Summary In laboratory choice experiments, receptive female western mosquitofish Gambusia affinis affinis (deprived of contact with males 30 days) preferred the larger of two males. When two males differing in size were placed with a receptive female, the larger was generally able to monopolize access to her, but not when the female was not receptive. In other experiments, a single male was placed with a receptive or non-receptive female. These experiments showed size-correlated differences in male mating behavior. Smaller males were more likely to chase non-receptive females and attempt to inseminate them forcibly, while larger males continued to court females even if they were non-receptive. Even when the female was receptive, there was some evidence of size-correlated differences in levels of courtship and chasing.     

Direct and indirect estimates of sperm precedence and displacement in the dragonfly Sympetrum danae (Odonata: Libellulidae)

Summary The non-territorial dragonfly Sympetrum danae shows a high degree of post-copulatory mate-guarding, which suggests precedence of the last male's sperm. Irradiated male techniques revealed that the last male that mates with a female fertilizes an average of 95% (100% in 28% of the cases) of the clutch laid immediately after copulation, irrespective of any previous matings. Sperm volume estimates in both sexes and sperm opacity changes in females at 7 stages of copulation and oviposition indicated that males remove 41–87% of previously deposited sperm from the female's storage organs during the first 5 min of the copulation. Ejaculation takes place during the remaining 10–15 min. We maintain that indirect estimates of precedence in libellulids, based on sperm volume changes, always understimate reality because of the supplementing effect of a first-in, last out mechanism. Because males are skilled at achieving sperm precedence, they are forced to be good guards as well, since a risk of take-overs exists. Females are believed to benefit from contact guarding because it results in a lowered risk of male harassment and predation as well as a lower energy expenditure during oviposition.     

Sperm transfer,displacement and precedence in Ischnura graellsii (Odonata : Coenagrionidae)

Summary Copulation in Ischnura graellsii may be divided into three stages, according to the movements and position of the male's abdomen. We measured sperm volumes in males and females interrupted at different phases of copulation in laboratory-reared and field specimens. The results showed that males remove sperm from the female during stage I, and do not transfer sperm until stage Il of the copulation. In the field females interrupted during stage I of copulation had less sperm than postcopula females, and the volume of sperm in laboratory females mated once or twice was similar. These results suggest that males can remove most of the sperm during stage I of copulation. Preparations of in-copula specimens showed the horns of the penis (used to remove sperm) inside the bursa copulatoox and the spermatheca. Therefore males can remove sperm from both organs, in contrast to the other Ischnura species so far studied, where males can empty only the bursa. The length of these horns is positively correlated with male body length, and there are significant differences in length between the left and right horns of individual males. This suggests great variability in the male's ability to remove sperm. On the other hand, ejaculate volume is positively related to male and female size, and negatively to male age. Males are likely to be able to detect the presence of sperm in females: if the effect of population density and time of start of copulation are taken into account, copulations are longer with mated than with virgin females. Using genetic markers, sperm precedence was studied by rearing the female offspring of 6 females mated with two males of different genotype. In 5 out of 6 crosses, the second male fertilized all the eggs laid by the female in her first clutch. On average, the following clutches were progressively more fertilized by the first male, but there were striking differences between crosses. These differences are probably due to the variability in the amount of sperm transferred and/or removed. Offprint requests to: A. Cordero     

Sperm motility and longevity in the giant cuttlefish, Sepia apama (Mollusca: Cephalopoda)

The sperm kinetics and fertilisation literature in marine invertebrates is heavily biased toward free-spawning species. Nonetheless, many species (e.g. cephalopods) transfer and/or fertilise gametes in confined external spaces or internally, creating very different selective pressures on sperm storage, sperm longevity and hence sperm competition. Here we report the results of an investigation into the effects of sperm age, water temperature and sperm concentration on sperm motility in the giant cuttlefish (Sepia apama). Significant positive correlations were found between percent motility and sperm concentration, and between sperm motile speed and sperm concentration. Mean percent motility of cuttlefish sperm suspension was still 9% eight hours after being released from the spermatophore and diluted into filtered seawater at 12°C (ambient field temperature during the spawning season). Sperm resuspended from spermatangia taken from (mated) females in the field were motile for up to 100 hours. When spermatophores were stored at 4°C motility was still observed in resuspended sperm after two months. Our results show that spermatangia and spermatophores can retain and release live sperm for long periods. The observed longevity of sperm in S. apama greatly increases the potential for sperm competition in this species.     

Sperm precedence, mating interval, and a novel mechanism of paternity bias in a beetle (Tenebrio molitor L.)

When females mate with more than one male, the ensuing sperm competition leads to the evolution of male mechanisms that skew paternity. Males of the yellow mealworm beetle (Tenebrio molitor) transfer a spermatophore to females during copulation, but sperm release and storage occur later. We investigated how the interval between two matings with different males affects sperm precedence by varying the interval between the copulations so that the second mating was either: (1) before sperm release from the first spermatophore (<5 min); (2) after sperm release but before spermatophore ejection (15–20 min); (3) after spermatophore ejection but before sperm storage (4 h), or (4) after complete sperm storage (24 h). We collected offspring over a period of 2 weeks and determined paternity by protein electrophoresis. There was second-male sperm precedence in all treatments, but when the interval was <5 min, the second male usually (86% of cases) had complete sperm precedence (i.e., P ₂=1). Investigations into the mechanism of second-male sperm precedence during <5-min mating intervals indicate that sperm release from the first spermatophore is inhibited, a phenomenon which has not been previously documented. Received: 31 January 2000 / Revised: 9 June 2000 / Accepted: 26 August 2000     

Heavy metal contamination and physiological variability in the Brazilian mangrove crabs Ucides cordatus and Callinectes danae (Crustacea: Decapoda)

 Physiological studies were made on the crabs Ucides cordatus (L.) and Callinectes danae sampled from populations living in “polluted” mangroves on the southeast littoral of Brazil. Analysis of Cu, Cd, Zn, and Fe of sediments and crab tissues showed interspecific differences in tissue concentrations, and significantly higher levels of Cu, Cd, and Zn in “polluted” populations compared to “unpolluted” crabs living in uncontaminated mangrove in the same geographical area. Individuals of both species from the polluted site showed significantly greater capacities for regulating blood osmotic concentrations at low salinity (9‰). However, U. cordatus showed a reduced hypo-regulatory ability in 34‰S. Differences in ionoregulation were also seen. “Polluted”C. danae showed significantly higher Na/ K-ATPase levels in posterior gills compared to “unpolluted” crabs. Oxygen consumption rates (M˙ _O2) were elevated in U. cordatus, but depressed in C. danae from the “polluted” population. Individuals of both species from this site showed significantly lower O:N ratios, mainly because of an increased net efflux of ammonia. Adenylate energy charge (AEC) values of muscle and hepatopancreas in “unpolluted” and “polluted” populations of both species were not significantly different. These physiological differences are discussed in relation to the known acute physiological and metabolic effects of heavy metals in crustaceans, and interpretated in the light of possible adaptive changes following long-term exposure to contamination. Received: 6 August 1999 / Accepted: 22 June 2000     

Fecundity and reproductive strategies in deep-sea incirrate octopuses (Cephalopoda: Octopoda)

Coleoid cephalopods show flexibility in their reproductive strategies or mode of spawning, which can range from simultaneous terminal spawning over a short period at the end of the animal’s life to continuous spawning over a long period of the animal’s life. Although a simultaneous terminal spawning strategy is typical of shallow water temperate octopuses, it is not known whether deep-sea octopods would have the same reproductive strategy. The reproductive strategies and fecundity were investigated in nine species of deep-sea incirrate octopuses: Bathypolypus arcticus, Bathypolypus bairdii, Bathypolypus ergasticus, Bathypolypus sponsalis, Bathypolypus valdiviae, Benthoctopus levis, Benthoctopus normani, Benthoctopus sp., and Graneledone verrucosa (total n = 85). Egg-length frequency graphs and multivariate analysis (principal components analysis) suggest that B. sponsalis has a synchronous ovulation pattern and therefore a simultaneous terminal spawning strategy. Although a simultaneous terminal spawning strategy is most likely for B. levis and B. normani, the egg-length frequency graphs and multivariate analysis also suggest a greater variation in egg-lengths which could lead to spawning over an extended period.     

Bioluminescence of deep-sea coronate medusae (Cnidaria: Scyphozoa)

Bioluminescence is the production of visible light by a living organism. The light commonly appears as flashes from point sources (involving one or more cells, usually described as photocytes) or as a glandular secretion. A visible flash usually involves synchronous light emission from a group of cells or, if from a single-celled organism such as a dinoflagellate, from a group of organelles. The number of cells (or organelles) responding synchronously is the main determinant of the flash intensity. Bioluminescence is a common phenomenon in many deep-sea animals and is widespread among the Cnidaria. In this paper, we compare and contrast in situ and laboratory recordings of the bioluminescent responses of specimens of the deep-sea scyphozoans Atolla wyvillei, Atolla vanhoffeni, Atolla parva, Nausithoe rubra, Paraphyllina intermedia, Periphyllopsis braueri and Periphylla periphylla. Displays in all seven species consist of localised flashes and propagated waves of light in the surface epithelium. The first few single waves propagate at rates of up to 60 cm s^-1 but subsequent ones in any sequence of stimuli gradually decrease in speed. After several single wave responses, a subsequent stimulus may elicit multiple waves that persist for several seconds. Following such a frenzy, the specimen becomes temporarily refractory to further stimuli, but if rested will recover its normal responses and may produce further frenzies. The dome area, situated above the coronal groove, of the genera Paraphyllina, Periphylla, and Nausithoe is covered with luminescent point sources. Such point sources are generally absent from the dome of species of Atolla. Captured specimens of A. parva also produce secretory bioluminescence, corroborating prior in situ observations of this ability. Secretory bioluminescence in P. periphylla takes the form of scintillating particles released from the lappet margins. We did not observe secretory displays in specimens of any other species in the laboratory, but one instance of apparent secretory luminescence was recorded in situ in a specimen of A. wyvillei.Communicated by J. P. Thorpe, Port Erin     

Pre-mating sperm removal in the bushcricket Metaplastes ornatus Ramme 1931 (Orthoptera, Tettigonoidea, Phaneropteridae)

Summary Mating in the bushcricket Metaplastes ornatus Ramme 1931 entails a number of peculiar genital couplings that precede the transfer of the large spermatophore. During these phase-I couplings, the male introduces his specially structured subgenital plate into the female's genital chamber, performs back-and-forth movements, and turns her genital chamber inside out when he withdraws, whereupon the female carefully cleans her everted genital chamber with her mouthparts. During the last coupling (phase II) the male's subgenital plate is not introduced but the large spermatophore, which averages 22% of a male's body weight, is transferred. Counts of sperm in the spermathecae of females suggested that the phase-I couplings, which occur prior to spermatophore transfer, function to remove, or at least to reduce, the sperm of a female's previous mates. The form of the keel of the male's subgenital plate, its position within the female's genital tract during phase-I couplings, and the back-and-forth movements suggest that the male may stimulate release of sperm from the female's spermatheca by a mechanism similar to fertilization as eggs pass through the genital chamber during oviposition.     

Lifetime mating success in a natural population of the damselfly,Enallagma hageni (Walsh) (Odonata: Coenagrionidae)

Summary Variance in lifetime mating success was measured for individuals of a population of Enallagma hageni, a non-territorial damselfly in northern Michigan. E. hageni is an explosive breeder with scramble competition for mates. Highly skewed operational sex ratios resulted in intense male-male competition which took the form of interference with tandem pairs. 41% of the males failed to mate in their lifetime as opposed to only 3.6% mating failure in females. The effect on mating success of size, age, longevity, and time spent at the breeding site were investigated. Intermediate sized males obtained the most matings, and male lifetime mating success was highly correlated with longevity.     

Effectiveness of the mating plug in Atrophaneura alcinous (Lepidoptera : Papilionidae)

Summary At mating, males of Atrophaneura alcinous plug the female copulatory duct with a secretory material, but some females copulate several times and can receive spermatophores from different males up to three times. Remating by plugged females mostly takes place shortly after the first mating, when the freshly formed first plug has not completely hardened. A freshly formed plug can be pressed aside or tunneled by the male aedeagus, and thus intromission and subsequent spermatophore transfer are sometimes possible. This is not always the case, however, and larger plugs are more likely to prevent aedeagus intrusion even if they are not completely hardened. Also, a few females remated a day after the first mating or later, when the first plug is already very hard. Completely hardened plugs are more effective than freshly formed ones; later mating males can thrust the aedeagus into the ductus bursae only when the plug is less than ca 1.2 mg (dry weight). The occurrence of female re-mating in plug-forming species thus does not necessarily mean that the plug is ineffective. Offprint requests to: K. Matsumoto     

Sperm precedence and sperm storage in multiply mated red flour beetles

In insects, the last male to mate with a female often gains access to a disproportionate number of subsequent fertilizations. This study examined last-male sperm precedence patterns in doubly and triply mated Tribolium castaneum females. Sperm storage processes were investigated by measuring the quantity of sperm stored within the female spermatheca following single, double, and triple matings. Both doubly mated and triply mated females exhibited high last-male sperm precedence for progeny produced during the first 48 h following the last mating, with females in both groups exhibiting parallel declines in sperm precedence 1 and 2 weeks later. The number of sperm stored by females increased by 33% between singly mated and doubly mated females, indicating that the spermatheca is filled to only two-thirds capacity following insemination by the first male. Based on the proportion of stored sperm from first and second matings, we tested predictions about sperm precedence values based on models of random sperm mixing. High initial last-male sperm precedence strongly supports stratification of last-male sperm. By 1–2 weeks after double matings, sperm precedence declined to levels indistinguishable from values expected under random mixing. These results provide insight into mechanisms of sperm storage and utilization in this species. Received: 20 August 1997 / Accepted after revision: 24 May 1998     

Alternative mating strategies in the water strider Gerris elongatus (Heteroptera,Gerridae)

Summary Males of the water strider Gerris elongatus established territories which included copulation and oviposition sites (small pieces of fallen bamboo). Males were aggressive and competition for territory and females was observed frequently. Male midlegs were more developed than female midlegs and were used as weapons. Reproductive behaviour changed as the breeding season advanced. Early in the season immature females were attracted by male surface wave courtship signals, then copulated white floating on the water surface without ovipositing (type 1). In midseason, males established territories, produced calling signals and attracted females which copulated and oviposited there with male postcopulatory guarding (type 2). In late season, many females oviposited without postcopulatory guarding on pondweed mats near fallen bamboo. Non-territorial males waiter for the arrival of these females and copulated without courtship, but mating success was low (type 3). These alternative mating strategies appeared to depend on differences in male size. Larger males were superior to smaller males in many ways (establishing territory, fighting, mating etc.). The largest males defended territories and had higher mating success than small non-territorial males. Medium sized males used all three strategies according to the number of empty territories and seasonal femald distribution.     

Sperm design and variation in the New World blackbirds (Icteridae)

Post-copulatory sexual selection (PCSS) is thought to be one of the evolutionary forces responsible for the rapid and divergent evolution of sperm design. However, whereas in some taxa particular sperm traits are positively associated with PCSS, in other taxa, these relationships are negative, and the causes of these different patterns across taxa are poorly understood. In a comparative study using New World blackbirds (Icteridae), we tested whether sperm design was influenced by the level of PCSS and found significant positive associations with the level of PCSS for all sperm components but head length. Additionally, whereas the absolute length of sperm components increased, their variation declined with the intensity of PCSS, indicating stabilising selection around an optimal sperm design. Given the diversity of, and strong selection on, sperm design, it seems likely that sperm phenotype may influence sperm velocity within species. However, in contrast to other recent studies of passerine birds, but consistent with several other studies, we found no significant link between sperm design and velocity, using four different species that vary both in sperm design and PCSS. Potential reasons for this discrepancy between studies are discussed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.