Sperm Limitation Research Articles

Sauger testicular harvest eliminates sperm limitation during large‐scale saugeye (Walleye × Sauger) production

AbstractObjectivePoor milt yield via strip‐spawning in male Sauger Sander canadensis limits the production of saugeye (female Walleye S. vitreus × male Sauger) by the Ohio Division of Wildlife. Compared to strip‐spawning, collecting sperm via testicular harvest offers several advantages that increase production efficiency through enhanced sperm yield (e.g., requires fewer broodfish, allows higher sperm application rates, and increases fertilization rates). The benefits of testicular harvest have been demonstrated experimentally in Sauger but not at a production scale. In this study, I validated the large‐scale efficacy of testicular harvest in Sauger for saugeye production.MethodsI collected sperm from male Sauger by using either testicular harvest (42 fish) or strip‐spawning (222 fish), diluted samples with extender, and combined samples to create 9‐mL sperm pools (n = 21 for testicular harvest; n = 39 for strip‐spawning). I compared sperm quantity, sperm motility, and production attributes (broodstock requirements, sperm application rates, and expected fertilization) between testicular harvest and strip‐spawning collection methods.ResultBoth collection methods resulted in high‐quality sperm. Testicular harvest doubled the sperm yield (total number of sperm) per 9‐mL pool despite using only 2 fish/pool, while strip‐spawning required 5–7 fish/pool. Through this enhanced yield, testicular harvest produced enough sperm to fertilize 317 L of eggs (1.06 mL/L) by using 80% fewer males than strip‐spawning. Further, sperm application increased fourfold using testicular harvest (4.23 mL/L) while still requiring 30–40% fewer fish than are currently used to meet production. Adopting testicular harvest for saugeye production in 2023 increased broodstock sperm yield, allowed greater sperm application rates, reduced Sauger broodstock needs, and increased saugeye hatching rates (15–20% increase).ConclusionTesticular harvest provides an efficient approach for sperm collection during large‐scale production in fish species that produce small quantities of sperm.

Spawning history, fecundity, and potential sperm limitation of female blue crabs in Chesapeake Bay

The blue crab (Callinectes sapidus) is an ecologically and economically important species in estuaries of the Western Atlantic Ocean and Gulf of Mexico. Given the importance of reproductive output and spawner demography on population dynamics, blue crab management may be improved if individual-based changes in egg production are identified and incorporated into management advice. We determined the spawning history, batch fecundity, and stored sperm quantity of 126 ovigerous blue crabs in 2022 to estimate the reproductive potential of female blue crabs in Chesapeake Bay. Our mean estimate of fecundity, 2.17 million eggs/female, is similar to a fecundity estimate from 1986 (2.6 million eggs/female), but lower than an estimate from 1987 (4.0 million eggs/female). The 1987 estimate was likely biased high due to methodological differences. In 2022, size-specific fecundity did not differ from that in 1986. Size-specific fecundity was lower by 0.28 million eggs in multiparous females (i.e., those that produced at least one previous egg mass) compared with primiparous females (i.e., those producing their first egg mass). Size-specific fecundity was also greater in July and August than in June, however, females in June had a greater capacity for future reproductive potential because their average stored sperm quantity was three times greater than that of females in July and August. Most females in June were primiparous and would become multiparous females in July and August with higher size-specific fecundity. Our study is the first to pair individual fecundity, stored sperm quantity, and spawning history for blue crabs, which allows for a robust assessment of reproductive potential. Generally, the reproductive potential of individual female blue crabs was high at the individual level, such that sperm limitation is unlikely at the population level. Population-level production may be increased by protecting primiparous spawners as these crabs have the highest capacity to contribute offspring to the population. Furthermore, fisheries management may be improved by using our updated estimate of size-specific fecundity (Fecundity = 268,337 × exp(0.015 × Carapace Width)) and incorporating month or spawner history in models of stock production.

Multiple mating does not benefit females of a polyandrous pollinating fig wasp

In some species, females vary in the numbers of times they mate. While polyandry will always be beneficial to a male that mate with a previously mated female, the effect on female fitness is unclear. From females' perspective, variation in matedness can reflect adaptive differences in females’ requirements for mating or non-adaptive chance factors. Pollinating fig wasps have been considered to be mostly monandrous although polyandry has been confirmed in a number of species. Here we first show that the pollinating fig wasp, Platyscapa awekei, is polyandrous. Second, we show that intraspecific variation in female matedness may be explained best by chance encounters between males and receptive females. The mean number of offspring does not increase with polyandry. Nor is there evidence of sperm limitation. These observations rule out direct benefits to females. Despite evidence for multiply-mated females having mated with less compatible males, multiple mating is not combined with selective preference for more compatible males' sperm, ruling out indirect benefits. Therefore variation in female matedness seems to have no fitness benefit to females and from the females' perspective may be best explained by chance variation in encounter rates between males and receptive females.

Kin selection in interactions between gametes: Gamete competition, gamete limitation, and sex allocation

Kin selection on one hand, and gamete interactions in post-ejaculatory sexual selection on the other are two major research themes that have risen to prominence over the past half century and have simultaneously developed into central fields of research in evolutionary biology. There is a natural connection between the two: when gametes interact with each other, very commonly many of them originate from the same parent and are thus siblings. For example, sperm competition will almost always involve competition between sibling gametes even if the interacting parents are not related to each other. If parents are related to each other, the relatedness between gametes increases further. Here we discuss the relation between kin selection on one hand, and gamete competition, gamete limitation, local gamete competition, and the evolution of sex allocation on the other. To illustrate these topics, we present a novel model on sex allocation in simultaneous hermaphrodites under sperm limitation and limited, costly dispersal. We find that sperm limitation can significantly increase allocation into male function, but limited dispersal (and thus increased relatedness) does not alter sex allocation regardless of the presence of sperm limitation.

Sexual conflict over phenological traits: selection for protandry can lock populations into temporally mismatched reproduction.

In seasonal environments, competition among males can drive males to emerge before females. Females, simultaneously, should avoid emerging at times after sufficient male availability. We show that the consequent sexual conflict over timing traits can produce arms races toward ever earlier emergence, if low mate-search efficiency or sperm limitation elevate the latter risk for females. In reality, however, arms races over timing cannot proceed indefinitely as this ignores the relevant ecological context for phenology: the temporal niche of resource availability for offspring development. We model the interaction of natural and sexual selection to predict the sexual conflict load, i.e., the loss of population fitness caused by sexual conflict. We show that selection to avoid matelessness can exacerbate another problem of maladaptation: a temporal mismatch between the organism (e.g., insect) and its resource (e.g., host plant). Load frequently associates with protandry if males can mate multiply, yet lack of multiple mating does not imply zero load. A temporal mismatch can still evolve, where both sexes emerge and mate suboptimally early with respect to the seasonal resource peak, because monogamy does not guarantee that every individual finds one mate, and selection favors early individuals in mate-finding contexts.

The impact of size truncation on reproductive success in the southern king crab (Lithodes santolla)

Sex-biased fishing mortality caused by male-only fishing may result in sperm limitation and recruitment overfishing. These effects can be observed by studying the size at functional reproduction (SFR) of lithodid females. We studied changes in the ratio of males to females, size truncation, and changes in SFR in the southern king crab (SKC) in two areas experiencing different fishing pressures in southern Chile. SFR was estimated with the Richards Function, a generalized 4-parameter logistic model. The shrinking of SFR of females may occur due to the proportional shrinking of reproductive and non-reproductive females and/or because the shape of the ogive changes, setting the inflection point back to smaller sizes. In the region with low fishing pressure the functional reproductive ogive was symmetric (γ = 1, and the asymptote was ∼1, indicating a balance in male availability. In the region with high fishing pressure γ was 82 % lower and the asymptote was 23 % lower, an indicator of sperm limitation. The symmetric shape of the logistic curve, which is widely assumed when fitting maturity ogives, is not the most appropriate assumption in SKC and possibly in other males-only crab fisheries. More general shapes of the ogive should be estimated and studied.

Evidence for Sperm Limitation in the Louisiana Blue Crab Spawning Stock

AbstractMale‐targeted fishing pressure has the potential to skew population sex ratios and to result in sperm limitation in females, where the quantity or quality of sperm received during mating is insufficient for the female to achieve her full lifetime reproductive potential. Blue crabs Callinectes sapidus are heavily targeted by commercial and recreational fisheries throughout much of their range, with fishing pressure biased toward males. Additionally, blue crabs are particularly susceptible to sperm limitation because mating occurs during a short window following the female’s terminal molt and stored sperm is used to fertilize all future broods. We investigated sperm quantities in recently molted and mated female blue crabs in southeastern Louisiana to assess the potential for sperm limitation in this area. Sperm quantities were an order of magnitude lower than those previously observed in other areas. Brood production modeling indicated that most of the female blue crabs in this region are heavily sperm limited and unable to achieve their lifetime spawning potential. On a population level, this sperm limitation may be partially responsible for recent declines in landings and estimates of abundance. Although insufficient data exist to assess the precise cause of this sperm limitation, these results should be incorporated into future stock assessments and management decisions for the Louisiana blue crab spawning stock.

Large males matter: Low sperm reserves in female snow crab (Chionoecetes opilio) off Newfoundland, Canada

Large, male snow crab (Chionoecetes opilio) off Newfoundland and Labrador were heavily exploited throughout their range from 2015 to 2018 leading to biological concerns about the possibility of sperm limitation within portions of the stock. To address this, primiparous females were sampled from six sites off the island of Newfoundland to gather data on their overall reproductive health (e.g., seminal receptacle load, SL, and clutch weight) at the end of this heavily exploited period. Snow crab females had low SLs in comparison to long-term monitoring at nearby sites in the Northern Gulf of St. Lawrence but were similar to historic observations from the Eastern Bering Sea. Seminal receptacle loads were significantly influenced by the female’s carapace width, time since mating (represented by sampling month), as well as site-specific characteristics of the male population (ratio of most competitive males in the population and male time since terminal molt). Clutch weight was significantly influenced by the female’s carapace width, as well as the average size of sexually mature males and the average time since terminal molt of adult males. Our findings show the potential for sperm limitation to occur in populations depleted of large-male snow crab and by extension for excessive fishing of males to diminish reproductive capacity of the stock. These findings highlight the importance of maintaining conservative exploitation rates for snow crab that protect a substantial proportion of large adult males in order to preserve reproductive capacity.

Sperm Limitation Produces Male Biased Offspring Sex Ratios in the Wasp, Nasonia vitripennis (Hymenoptera: Pteromalidae)

Haplo-diploid sex determination in the parasitoid wasp, Nasonia vitripennis (Walker), allows females to adjust their brood sex ratios. Females influence whether ova are fertilized, producing diploid females, or remain unfertilized, producing haploid males. Females appear to adjust their brood sex ratios to minimize ‘local mate competition,’ i.e., competition among sons for mates. Because mating occurs between siblings, females may optimize mating opportunities for their offspring by producing only enough sons to inseminate daughters when ovipositing alone, and producing more sons when superparasitism is likely. Although widely accepted, this hypothesis makes no assumptions about gamete limitation in either sex. Because sperm are used to produce daughters, repeated oviposition could reduce sperm supplies, causing females to produce more sons. In contrast, if egg-limited females produce smaller broods, they might use fewer sperm, making sperm limitation less likely. To investigate whether repeated oviposition and female fertility influence gamete limitation within females, we created two treatments of six mated female wasps, which each received a series of six hosts at intervals of 24 or 48 h. All females produced at least one mixed-sex brood (63 total broods; 3,696 offspring). As expected, if females became sperm-limited, in both treatments, brood sex ratios became increasingly male-biased with increasing host number. Interhost interval did not affect brood size, total offspring number, or sex ratio, indicating females did not become egg limited. Our results support earlier studies showing sperm depletion affects sex allocation in N. vitripennis¸ and could limit adaptive sex ratio manipulation in these parasitoid wasps.

Sperm metabolic rate predicts female mating frequency across Drosophila species.

Female mating rates vary widely, even among closely related species, but the reasons for this variation are not fully understood. Across Drosophila species, female mating frequencies are positively associated with sperm length. This association may be due in part to sperm limitation, with longer-spermed species transferring fewer sperm, or to cryptic female choice. However, a previously overlooked factor is sperm metabolic rate, which may correlate with sperm length. If faster-metabolizing sperm accumulate age-related cellular damage more quickly, then females should remate sooner to obtain fresh sperm. Alternatively, frequent female mating may select for increased sperm competitiveness via increased metabolism. Here, we measure sperm metabolism across 13 Drosophila species and compare these measures to published data on female mating rate and on sperm length. Using fluorescent lifetime imaging microscopy, we quantify NAD(P)H metabolism ex vivo, in intact organs. Phylogenetically controlled regression reveals that sperm metabolic rate is positively associated with sperm length and with female mating frequency. Path analysis shows sperm length driving sperm metabolism and sperm metabolism either driving or being driven by female mating rate. While the causal directionality of these relationships remains to be fully resolved, and the effect of sperm metabolism on sperm aging and/or sperm competitiveness remains to be established, our results demonstrate the importance of sperm metabolism in sexual selection.

Density-dependent patterns of multivariate selection on sperm motility and morphology in a broadcast spawning mussel.

Sperm cells exhibit extraordinary phenotypic variation, both among taxa and within individual species, yet our understanding of the adaptive value of sperm trait variation across multiple contexts is incomplete. For species without the opportunity to choose mating partners, such as sessile broadcast spawning invertebrates, fertilization depends on gamete interactions, which in turn can be strongly influenced by local environmental conditions that alter the concentration of sperm and eggs. However, the way in which such environmental factors impact phenotypic selection on functional gamete traits remains unclear in most systems. Here, we analyze patterns of linear and nonlinear multivariate selection under experimentally altered local sperm densities (densities within the capture zone of eggs) on a range of functionally important sperm traits in the broadcast spawning marine mussel, Mytilus galloprovincialis. Specifically, we assay components of sperm motility and morphology across two fertilization environments that simulate either sperm limitation (when there are too few sperm to fertilize all available eggs), or sperm saturation (when there are many more sperm than required for fertilization, and the risk of polyspermy and embryonic failure is heightened). Our findings reveal that the strength, form, and targets of selection on sperm depend on the prevailing fertilization environment. In particular, our analyses revealed multiple significant axes of nonlinear selection on sperm motility traits under sperm limitation, but only significant negative directional selection on flagellum length under sperm saturation. These findings highlight the importance of local sperm densities in driving the adaptation of sperm phenotypes, particularly those related to sperm motility, in broadcast spawning invertebrates.

Bifurcation analysis of the predator\u2013prey model with the Allee effect in the predator

The use of predator–prey models in theoretical ecology has a long history, and the model equations have largely evolved since the original Lotka–Volterra system towards more realistic descriptions of the processes of predation, reproduction and mortality. One important aspect is the recognition of the fact that the growth of a population can be subject to an Allee effect, where the per capita growth rate increases with the population density. Including an Allee effect has been shown to fundamentally change predator–prey dynamics and strongly impact species persistence, but previous studies mostly focused on scenarios of an Allee effect in the prey population. Here we explore a predator–prey model with an ecologically important case of the Allee effect in the predator population where it occurs in the numerical response of predator without affecting its functional response. Biologically, this can result from various scenarios such as a lack of mating partners, sperm limitation and cooperative breeding mechanisms, among others. Unlike previous studies, we consider here a generic mathematical formulation of the Allee effect without specifying a concrete parameterisation of the functional form, and analyse the possible local bifurcations in the system. Further, we explore the global bifurcation structure of the model and its possible dynamical regimes for three different concrete parameterisations of the Allee effect. The model possesses a complex bifurcation structure: there can be multiple coexistence states including two stable limit cycles. Inclusion of the Allee effect in the predator generally has a destabilising effect on the coexistence equilibrium. We also show that regardless of the parametrisation of the Allee effect, enrichment of the environment will eventually result in extinction of the predator population.

Reproductive changes in Foveaux Strait Ostrea chilensis, Southern New Zealand, after Bonamia exitiosa epidemics

ABSTRACT The commercially significant Foveaux Strait Ostrea chilensis fishery has been typified by consistently low brooding rates and recruitment failures since recurrent mass mortalities from Bonamia exitiosa infection. The present study examined the gametogenic cycle of Foveaux Strait O. chilensis monthly, from July 2017 to September 2018, using histological examination of the gonad and condition indices to determine resulting changes to gametogenesis, spawning, brooding, and spatial variation, compared to an initial study of reproduction before B. exitiosa epidemics. The seasonal gametogenic cycle and brooding period were similar to previous descriptions. However, there was evidence for a more female skewed sex ratio, and the development and release of ova into the mantle cavity at smaller sizes. Despite similarities in gametogenesis, sex ratios, temperature, and chlorophyll-a concentrations between five sites across Foveaux Strait, the western-most site had no brooders and consistently lower condition indices, compared to the eastern-most site. Oysters may need to be in sufficient condition to initiate brooding, and reduced male densities may contribute to sperm limitation, which, along with a disconnect between the peak release of gametes and brooding, may have contributed to lower brooding rates.

Multiple Mating of Aphelinus asychis Enhance the Number of Female Progeny but Shorten the Longevity.

Simple SummaryAphelinus asychis Walker is an arrhenotocia endoparasitoid against the devastating vegetable pest Myzus persicae. Unmated Aphelinus asychis females only produce male progeny, and mated female adults produce male and female progeny. Because only female adults can kill the target pest by parasitism and feeding, the control efficiency of Aphelinus asychis was mainly affected by the percentage of female adults. We found that Aphelinus asychis females could mate multiple times to receive more sperm in their life span, which was beneficial for enhancing the number and percentage of female progeny. In addition, backcrossing is critical for population increase when the proportion of males is low. We also found that there was no significant difference in the population fitness of Aphelinus asychis between backcross and control treatments.The Aphelinus asychis female adult is an important arrhenotocous parthenogenesis parasitoid of Myzus persicae, and its reproductive mode is beneficial for the population continuation of A. asychis by way of multiple mating and backcross. To explore the effect of mating on the population fitness and control efficiency of A. asychis, its mating frequency and backcross were observed under laboratory conditions. The results showed that most matings in A. asychis involved four distinct stages: courtship, pre-copulatory, copulation, and post-copulatory behaviours. Only the duration of courtship increased significantly with an increase in copulation frequency for females, and the courtship duration of A. asychis females mated with different males were significantly shorter than those mated with the same male at the same mating times, which suggested that A. asychis females might prefer to mate with different males to enrich the genotype of their offspring. The total number of mummified aphids and the female and male longevity decreased significantly with an increase in mating frequency. On the contrary, female progenies increased significantly with an increase of mating frequency, suggesting that sperm limitation might occur in females when they only mated once. These results imply that females might prefer to receive more sperm by mating multiple times in their life span. In addition, we found that the intrinsic rate of increase (r) of A. asychis of the control group (0.2858 d−1) was significantly greater than that in the backcross treatment (0.2687 d−1). The finite killing rate (θ) of A. asychis of the control group was similar to that in the backcross treatment, which showed that this treatment had a negligible negative effect on the control efficiency of A. asychis. In conclusion, the results showed that multiple mating increased the number and proportion of A. asychis female progenies but shortened the longevity of female and male adults, while the negative effect of backcross on the control efficiency of A. asychis was negligible.

Does recent experience affect large male advantage in a sequentially-mating fish?

Abstract In many mating systems, large male body size is associated with dominance in direct contests with rivals and females may exhibit preference for larger males. As such, body size is often positively associated with mating success. However, mating experience can influence the potential advantage of large body size through alterations in behaviour and depletion of sperm reserves. In Japanese medaka (Oryzias latipes), males mate with many females each day, and larger males mate more frequently than smaller males. In an observational experiment, we tested the following alternate predictions: (1) recent mating experience may enhance mating success through a carry-over effect of prior mating, whereby small experienced males gain an advantage over large inexperienced rivals in mating contests; or (2) recent mating experience decreases mating success through a reduction in fertilization due to sperm limitation, effectively dampening the large-male advantage against a small inexperienced rival. We examined the interactive effect of size and recent experience on mating behaviour and success. While mating contests were monopolized by large males, recent experience enhanced mating success, especially in small male winners. Experienced males courted more readily than those without recent experience, suggesting that recent prior mating enhances this behaviour. Furthermore, males who had copulated recently did not exhibit sperm depletion when in the presence of a competitor, nor did female behaviour indicate a preference for inexperienced males. This suggests that males can use sexual experience to increase their reproductive success in future mating situations, which may influence the action of sexual selection and alternative tactics in shaping mating systems.

Female reproductive output and potential recruitment of three fished southern king crab stocks from the Southern Atlantic Ocean

Abstract The female reproductive output and potential recruitment (PR) were studied in three Argentinean southern king crab (Lithodes santolla and Lithodes confundens) stocks: in the Beagle Channel (BC), under an artisanal fishery pressure since 1930; in the San Jorge Gulf (SJG), under 10-years industrial fishing exploitation; and off the Atlantic coast of Isla Grande de Tierra del Fuego (TDF), under current exploratory regime. After evaluating their reproductive parameters, we suggest that these fisheries pass through at least two detectable phases. The first phase, in the SJG stock, is sperm limitation evidenced by a high proportion of ovigerous females but a decreased female fecundity. A second phase, in the BC stock, shows a sustained low proportion of ovigerous females which were the largest females of this stock, along with a decreased relative abundance, which in lithodids are indicators of recruitment overfishing. Contrastingly, the TDF stock showed healthy population parameters before the opening of the exploratory fishery. The extremely low value of PR (2.6%) in the bc stock further reinforces that this stock is experiencing or has experienced recruitment overfishing, as a small proportion of the offspring would reach sexual maturity or achieve legal sizes.

Differences in prevalence of multiple paternity in the spiny spider crabMaja brachydactylain two localities that differ in female fecundity, fishing intensity, and management measures

AbstractMany marine species are under high fishing pressure, which can cause alterations in their mating systems and the structure of their populations. The spiny spider crab Maja brachydactyla is a commercial decapod on the east Atlantic coast. In Galicia, the most exploited region in Spain, the landing of ovigerous females is prohibited, favouring exploitation focused on males. The removal of males, especially the largest ones, may lead to sperm limitation and a reduction in the average size over generations. In these cases, polyandry can work as a mechanism to protect females against sperm limitation and to increase genetic diversity and effective population size. This study analyses the multiple paternity in M. brachydactyla in two localities that differ in female fecundity, fishing intensity, and management measures. Our results showed multiple paternity in this species for the first time, with a moderate bias between sires. However, the frequency of multiple paternity was almost seven times higher in the intensely exploited Golfo Ártabro (NW Spain; 69%) than in Carna (W Ireland; 10%), where exploitation levels and female fecundity are lower.

Multilevel Selection on Offspring Size and the Maintenance of Variation.

AbstractMultilevel selection on offspring size occurs when offspring fitness depends on both absolute size (hard selection) and size relative to neighbors (soft selection). We examined multilevel selection on egg size at two biological scales-within clutches and among clutches from different females-using an external fertilizing tube worm. We exposed clutches of eggs to two sperm environments (limiting and saturating) and measured their fertilization success. We then modeled environmental (sperm-dependent) differences in hard and soft selection on individual eggs as well as selection on clutch-level traits (means and variances). Hard and soft selection differed in strength and form depending on sperm availability-hard selection was consistently stabilizing; soft selection was directional and favored eggs relatively larger (sperm limitation) or smaller (sperm saturation) than the clutch mean. At the clutch level, selection on mean egg size was largely concave, while selection on within-clutch variance was weak but generally negative-although some correlational selection occurred between these two traits. Importantly, we found that the optimal clutch mean egg size differed for mothers and offspring, suggesting some antagonism between the levels of selection. We thus identify several pathways that may maintain offspring size variation: environmentally (sperm-) dependent soft selection, antagonistic multilevel selection, and correlational selection on clutch means and variances. Multilevel approaches are powerful but seldom-used tools for studies of offspring size, and we encourage their future use.

Ovary resorption in the Norway lobster (Nephrops norvegicus) and its possible causes with special reference to sperm storage

The Norway lobster, Nephrops norvegicus, is an important fisheries species in the North-East Atlantic area. In some circumstances, mature females of Nephrops norvegicus can resorb their ovary rather than completing spawning, but the implications of this phenomenon to reproductive biology and fisheries sustainability are not known. To understand after effects of ovary resorption, we studied long-term demographic data sets (1994–2017) collected from the western Irish Sea and the North Sea. Our considerations focused on potential correlations among the frequency of resorption, female insemination, and body size of resorbing females. Resorption was continuously rare in the western Irish Sea (less than 1%); whereas much higher rates with considerable year-to-year variation were observed in the North Sea (mean 9%). Resorption started in autumn after the spawning season (summer) had passed. The frequency stayed high throughout winter and declined again in spring. As sperm limitation can occur in male-biased fisheries, we expected a lack of insemination could be responsible for resorption, but affected females were indeed inseminated. Resorbing females were significantly larger than other sexually mature females in the North Sea, but the opposite trend was observed in the western Irish Sea. It is therefore possible that other, environmental factors or seasonal shifts, may trigger females to resorb their ovaries instead of spawning. Resorption may as well represent a natural phenomenon allowing flexibility in the periodicity of growth and reproduction. In this sense, observations of annual versus biennial reproductive cycles in different regions may be closely linked to the phenomenon of ovary resorption.

A novel method of quantifying sperm to determine the potential for sperm depletion in male American lobstersHomarus americanus(H. Milne Edwards, 1837) (Decapoda: Astacidea: Nephropidae)

AbstractSperm limitation is a concern for a number of heavily fished decapods; however, work to assess this concern is sometimes hampered by a lack of simple techniques to quantify sperm transferred during reproduction. Our primary goal was to determine if DNA measurements could be used to quantify the sperm content of spermatophores and thus facilitate investigations of sperm limitation in American lobsters (Homarus americanus H. Milne Edwards, 1837). This was achieved by measuring the amount of DNA in a sample and then calibrating those values by using flow cytometry to count the number of individual sperm present in the sample. Our results show that the DNA quantification technique provides a fast and accurate way to quantify sperm. We then demonstrated the utility of the method by using it to examine the rate at which males can produce sperm under simulated conditions of repeated mating events, a situation that might lead to a reduction in the number of sperm per spermatophore. While spermatophores obtained from male lobsters at three-day intervals varied substantially in the number of sperm they contained (range 427,090–5,028,996; mean 2,306,473), there was no clear decline in sperm count over time. These results suggest that male lobsters replenish their sperm supplies rapidly, and that sperm recharge rate is unlikely to be a factor that could lead to sperm limitation in American lobster populations.