Functional morphology of the female reproductive system of a crab with highly extensible seminal receptacles and extreme sperm storage capacity

We studied the functional morphology of the female reproductive system of the purple stone crab Danielethus crenulatus . The most remarkable feature is the relative storage capacity and extensibility of the seminal receptacles. These receptacles are a pair of simple sacs that lack internal structures dividing the internal lumen. Differences in seminal receptacle size and contents are accompanied by conspicuous changes in receptacle lining at a tissue level. Full seminal receptacles contain discrete sperm masses formed by hardened fluid and densely packed spermatophores. Different sperm masses are likely from different mates and their stratified disposition within the seminal receptacles is compatible with rival sperm displacement and last sperm precedence. Additionally, the anatomical structure of the vulva and vagina suggest active female control over copula. We discuss our results in the general context of sperm storage in brachyurans and the implications for the mating system of this species.     

The journey of squid sperm

Sperm storage is common in internally fertilizing animals, but is also present in several external fertilizers, such as many cephalopods. Cephalopod males attach sperm packets (spermatangia) to female conspecifics during mating. Females of eight externally fertilizing families comprising 25% of cephalopod biodiversity have sperm-storage organs (seminal receptacles) in their buccal area, which are not in direct physical contact with the deposited spermatangia. The mechanism of sperm transmission between the implantation site and the storage organ has remained a major mystery in cephalopod reproductive biology. Here, jumbo squid females covering almost the entire life cycle, from immature to a laboratory spawned female, were used to describe the internal structure of the seminal receptacles and the process of sperm storage. Seminal fluid was present between the spermatangia and seminal receptacles, but absent in regions devoid of seminal receptacles. The sperm cellular component was formed by spermatozoa and round cells. Although spermatozoa were tracked over the buccal membrane of the females to the inner chambers of the seminal receptacles, round cells were not found inside the seminal receptacles, suggesting that spermatozoa are not sucked up by the muscular action of the seminal receptacles. This finding supports the hypothesis that spermatozoa are able to actively migrate over the female skin. Although further experimental support is needed to fully confirm this hypothesis, our findings shed light on the elusive process of sperm storage in many cephalopods, a process that is fundamental for understanding sexual selection in the sea.     

Sperm competition and reproductive success in the decapod Inachus phalangium (Majidae): a male ghost spider crab that seals off rivals' sperm

Parker's (1970a) hypothesis that the overlap of multiple mating sperm in the female's storage organs promotes sperm competition is tested here for the first time in Crustacea: specifically, the mechanisms and consequences of sperm competition are detailed for the spider crab Inachus phalangium . Females of this species store ejaculates from successive copulations with different males discretely and consecutively in sac-like twin seminal receptacles. During copulation males transfer a large quantity of a sperm-free seminal plasma, followed by the sperm which is stored in small spermatophores and forms a densely-packed sperm packet. It was shown, using ³H-thymidine-labelled ejaculate, that the last male to mate displaces the ejaculate of his predecessors dorsally into the apex of the receptacle. Sperm of previous matings are sealed in with the hardening seminal plasma (sperm gel) and are thus prevented from being used to fertilize eggs, while the last male to mate places his sperm closest to the oviduct and vaginal openings. In experiments using the 'sterile-male' method, sperm from the last male to mate gained all fertilizations in subsequent broods. The seminal plasma forms the sperm gel in ghost spider crabs which is used for displacement of previously stored sperm, whereas various other brachyuran taxa use seminal plasma to produce the sperm plug, which prevents a male's sperm from being displaced.     

Locomotor activity pattern in pairs of the subsocial desert isopod Hemilepistus reaumurii

Locomotor activity rhythm of fresh adult of H. reaumurii was recorded in pairs with ovigerous and with non-ovigerous females. According to double-plotted actograms and waveform curves, results showed the presence of different locomotor patterns. In fact, locomotor profiles of pairs with ovigerous females were mainly bimodal whatever the recording conditions, whereas locomotor patterns were trimodal in pairs with non-ovigerous females. Results showed also that locomotor activity rhythm was more stable in the presence of the synchronizer (nLD cycle) than in constant darkness whatever the recording type. Moreover, the most important stability of the locomotor rhythm was observed under constant darkness and individuals were more active in pairs with ovigerous females than in pairs with non-ovigerous females.     

Temperature influences the reproduction of fiddler crabs at the southern edge of their distribution

Understanding the spatial patterns of reproductive biology might provide predictions about fitness and population stability in different locations within the geographical range of a particular species. Leptuca uruguayensis is a fiddler crab that breeds year round in tropical estuaries but only in summer months in temperate salt marshes. In this study, we examined several reproductive attributes of the southernmost population of L. uruguayensis, including the proportion of ovigerous females, the proportion of surface‐active crabs, the developmental status of the gonads and hepatopancreas, and the fullness of seminal receptacles, and related them to environmental factors such as temperature, photoperiod, and sediment organic matter content. We found that temperature was the environmental factor that was most correlated with the reproductive process of the southernmost fiddler crab, since this environmental factor was related to ovarian development, to the fullness of seminal receptacles, and to the hepatosomatic index. At the southern edge of its distribution, the low temperatures of winter restricted reproduction in L. uruguayensis. These winter temperatures might represent the lower limit of the thermal window of this fiddler crab, limiting its extension toward higher latitudes.     

Male reproductive strategy in Trichogramma evanescens: sperm production and allocation to females

Abstract.  The production and allocation of sperm among successive mates during a male's life largely determine its fitness. The sperm production pattern and sperm allocation to females is studied in Trichogramma evanescens , a short-lived egg parasitoid of several lepidopteran species. At emergence, virgin males have an average of 1607 ± 249 sperm stored in the seminal vesicles and no further production occurs during adult life. These males are able to mate with at least 20 females in rapid succession. During the first 10 matings, the males transfer approximately 100 sperm each time and then transfer fewer and fewer sperm per mating. The number of sperm stored in spermathecae of successively mated females remains relatively constant for the first 10 females, and decreases slowly for the subsequent females. The relationship between male reproductive strategy and some life-history traits are discussed.     

The ontogeny of the female reproductive system in the parasitic castrator pea crab Calyptraeotheres garthi: Implications for its mating system

The knowledge of the mating system of pea crabs is still fragmentary as it remains dubious whether females copulate in the juvenile and free‐living ‘hard’ or in the obligatory symbiotic stages (adult stage ‘V’ or intermediate stages II to IV). To discriminate between these two possibilities, we analysed the female seminal receptacles, vagina and opercula, and the sperm content in different stages of the pea crab Calyptraeotheres garthi. Our histology and scanning electron microscopy results revealed that in the hard stage the seminal receptacle is simple without secretory epithelia, and vagina and opercula are not controlled by musculature. In stages II to IV, the seminal receptacles, vagina, and opercula are under development and these structures reach maturity in stage V. These results suggest that females become receptive in stage V and not during predating stages. We found no spermatozoa in SR of ‘hard’ and stage II to IV females while these structures were loaded of sperm in most stage V, indicating that females start to mate in stage V. Our results support the notion that males of C. garthi roam among hosts in search for sedentary stage V females, as predicted by Baeza and Thiel's ( 2007 ) model of mating systems for symbiotic crustaceans. Nevertheless, we failed to reveal whether females mate repeatedly: the accumulation of sperm in larger females might indicate occurrence of multiple copula or a high variability in male sperm transfer.     

A hypothesis about the origin of sperm storage in the Eubrachyura, the effects of seminal receptacle structure on mating strategies and the evolution of crab diversity: How did a race to be first become a race to be last?

The origins and evolution of sperm storage in Brachyura are enigmatic: sperm is either stored in seminal receptacles, accessible via the vulvae on the sixth thoracic sternite, or in spermathecae at the border between the seventh and eighth sternites. Crabs with spermathecae are collectively referred to as “podotremes” while crabs with seminal receptacles belong to the Eubrachyura. The position of gonopores is the primary basis for subdividing the Eurachyura into the Heterotremata (female vulvae + males with coxal gonopores) and Thoracotremata (female vulvae + males with sternal gonopores). We present a hypothesis about the evolution of seminal receptacles in eubrachyuran female crabs and argue that the sternal gonopore has been internalized into chitin-lined seminal receptacles and the vulva is in fact a secondary aperture. The loss of some or all of the ancestral chitinous seminal receptacle lining was linked to ventral migration of the oviduct connection. Male and female strategies are to maximize gamete fertilization. The most important variable for females is sperm supply, enhanced by long-term storage made possible by the seminal receptacle. To maximize their fertilization rates males must adapt to the structure of the seminal receptacle to ensure that their sperm are close to the oviduct entrance. The major evolutionary impetus for female mating strategies was derived from the consequences of better sperm conservation and the structure of the seminal receptacle. The advantages were all to the females because their promiscuity and sperm storage allowed them to produce more genetically variable offspring, thereby enhancing variation upon which natural selection could act. We extend our arguments to Brachyura as a whole and offer a unifying explanation of the evolution of seminal receptacles, comparing them with the spermathecae found in “Podotremata”: they were independent solutions to the same problem: maintaining sperm supply during evolutionary carcinization.Explanation of eubrachyuran mating strategies requires analysis of the mating–moulting link, indeterminate vs. determinate growth format and seminal receptacle structure. Two alternatives for each of these characters means that there are eight possible outcomes. Six of these outcomes have been realized, which we term Portunoid, Majoid, Eriphoid, Xanthoid, Cancroid, and Grapsoid–Ocypodoid strategies, respectively. Mapping these characters on to a workable phylogeny (wherein some changes to the seminal receptacle + moulting–mating links are assumed to have occurred more than once) produces the following relationships: Portunoids + Majoids are a sister group to the rest of the Eubrachyura, which fall into two sister groups, Eriphoids + Xanthoids and Cancroids + Grapsoid–Ocypodoids and the “Podotremata” is sister group to all the Eubrachyura. We conclude that what began as a race to be the first to mate was turned on its head to become a race to be last, by the evolutionary changes to the seminal receptacle. Eubrachyuran females were advantaged by greater reproductive autonomy, more opportunity to mate with other males, resulting in more genetically variable progeny and leading to the evolution of much greater taxonomic diversity compared to “podotremes”.     

Effects of seminal vesicle removal on fertility and uterine sperm motility in the house mouse

The relative significance of the accessory glands of the male reproductive tract in fertility is unclear. To clarify the role of the seminal vesicles, fertility and uterine sperm motility were determined before and after removal of seminal vesicles in the house mouse. After removal of seminal vesicles, the pregnancy rate (number of females pregnant/number of females X 100) was reduced and the time to birth was increased, while the average litter size was not changed. Fertilization, determined by examining the oocytes 30 h after mating, was highly variable after matings with males whose seminal vesicles were removed; in some cases none of the oocytes were fertilized. The motility of sperm recovered from the uterus 1 h after matings with males before and after seminal vesicle removal and sham operations was analyzed using a videomicrographic system. The motility of uterine sperm was less progressive with more lateral displacement of the head about the trajectory and a less linear trajectory after removal of the seminal vesicles. Sham-operated animals showed no consistent changes in motility of uterine sperm. The changes in sperm motility could contribute to the reduction in fertilization since sperm motility is necessary for transport in the female reproductive tract and interaction with the oocytes.     

No material benefits, and a fertilization cost, for multiple mating by female leaf beetles

When females mate multiple times it presents an intriguing problem for evolutionary biologists due to the high costs and not very apparent benefits. Yet, this behaviour must have higher benefits than costs to be maintained by natural selection. We studied possible benefits for multiple mating by female leaf beetles, Leptinotarsa decemlineata, both with multiple males (polyandry) and multiple times with the same male (repeated matings). For polyandry, we tested the material benefits hypothesis, as well as fertility insurance, by mating females to varying numbers of males and looking at sperm received and fecundity. Although there was a relationship between amount of stored sperm and number of matings, we did not find the predicted positive relationship between fecundity and number of matings. Thus, the material benefits hypothesis was not supported. For repeated matings, we tested the sperm and nonsperm material benefit hypotheses by mating females to a single male varying numbers of times on one mount. For this set of tests neither sperm number nor fecundity was positively correlated with number of matings, therefore neither hypothesis was supported. Interestingly, in both experiments, there was a significant decrease in hatch rate with an increase in matings, demonstrating a cost of polyandry. These findings, along with previous research, suggest a cost of multiple mating with a possible role of seminal fluids in the reduction in female fecundity.     

Remating, sperm transfer, and sperm displacement in the cactophilic species Drosophila buzzatii Patterson & Wheeler (Diptera: Drosophilidae)

The mating system of Drosophila buzzatii is characterized by short copulation duration, frequent remating in both males and females, and male ejaculate partitioning. Additional features of the system are strong sperm displacement and a high frequency of sterile matings. Remating frequencies and the effects of remating on various mating parameters were studied. In order to characterize variation, five isofemale lines from geographically distant localities in Australia (three localities), Brazil and the Canary Islands were used. Mating parameters studied were: premating time, copulation duration, interval between successive matings, and progeny number as a measure of sperm transfer. Variation for sperm displacement was studied in crosses between laboratory stocks and a number of isofemale lines from Australia. There were significant between‐line differences in female remating frequencies, premating time, copulation duration, interval between successive matings, and progeny numbers, indicating genetic variation for these traits. Females from the five lines mated on average 1.6 to 3.1 times in 4 h, with a maximum of eight matings for one female. The males were given a maximum of ten virgin females in sequence and more than one‐third of the males mated all ten females in the 2 h observation period. Copulation duration decreased and interval between matings increased with copulation number in multiply mated males. Mean copulation duration was c. 2 min. Sperm transfer, measured as the average number of progeny from a single mating, was low (c. 25) and multiply mated females gave more progeny than single mated females, although with much lower progeny numbers than observed in wild‐caught non‐virgin females. A surprisingly high proportion of observed matings gave no progeny, i.e. they were sterile matings. Sperm displacement was strong in most crosses and remained strong in multiply mated females. The results are discussed in relation to the evolution of mating patterns in Drosophila.     

Impact of male mating history on the temporal sperm dynamics of Choristoneura rosaceana and C. fumiferana females

In the oblique-banded leafroller, Choristoneura rosaceana, and the spruce budworm, C. fumiferana, male reproductive performance decreases with consecutive matings. While the onset time of mating did not vary, the time spent mating was longer in mated than in virgin males. Furthermore, a decline observed in the spermatophore mass with successive matings was associated with a concomitant decline in its apyrene and eupyrene spermatozoa content. In the hours following mating, spermatozoa migrate from the spermatophore, located in the bursa copulatrix, to the spermatheca. Regardless of the male's previous mating history, the number of apyrene sperm dropped rapidly in the days following mating whereas the number of eupyrene spermatozoa declined gradually. As the temporal pattern of sperm movement was similar in all treatments, females mated with previously-mated males would suffer from sperm shortage sooner than those mated with virgins. Large C. rosaceana females stored more apyrene spermatozoa in their spermatheca than small ones, irrespective of the time after mating or male mating history, while only large females mated with once-mated males received more apyrene sperm and accessory gland secretions than small ones mated with virgin or twice-mated males. The results obtained in this study are discussed in relation with their potential impact on the reproductive success of both sexes.     

Functional anatomy of the female reproductive systems of two spider crabs (Decapoda,Majoidea)

To better understand the mating systems of majoid crabs, we studied the functional anatomy of the female reproductive systems of the spider crabs Leurocyclus tuberculosus and Libinia spinosa, comparing them with those of other Majoidea. Adult females were measured and dissected, and their reproductive systems described macroscopically and histologically. In females of both species, the seminal receptacles are paired globular structures of ecto‐mesodermal origin. The mesoderm‐derived region is lined by a stratified epithelium. The anchoring, proliferative, and secretory strata are clearly recognizable . The ectoderm‐derived region is lined by a simple cylindrical epithelium underlying a cuticle that increases in thickness toward the vagina. The transition between the ectoderm and mesoderm‐derived regions is abrupt, with differences between the studied species: Li. spinosa has a “velum,” whereas Le. tuberculosus presents prominent “folds.” In both species, the position in which the oviduct is connected to the seminal receptacles is intermediate between the dorsal and ventral types previously described in other eubrachyurans. The seminal receptacles of the studied species show four different conditions, which can be distinguished macroscopically based on their shape and amount of sperm stored. We compare our data with those from other Majoidea in an attempt to determine whether the morphology of the seminal receptacles is related to different mating strategies or behaviors.     

The Effect of Repeated Matings on Sperm Numbers in Successive Ejaculates of the Cabbage White Butterfly Pieris rapae (Lepidoptera: Pieridae)

The effect of repeated matings on sperm numbers in successive ejaculates of the cabbage white butterfly, Pieris rapae, was examined. First ejaculates were larger than successive ones, which did not differ among themselves. Moreover, the cumulative mass of previous spermatophores was not correlated with that of the last mating. The number of eupyrene sperm bundles in the ejaculate did not differ between first and successive matings. Multiplying by 256, a male transfers about 11,000 eupyrene sperm at every mating. First ejaculates contained about 46,000 apyrene sperm, whereas successive ejaculates contained higher numbers. The sperm density increased after the first mating, though the spermatophore mass decreased. The significance of change in sperm quantity with mating number is discussed from the viewpoint of male investment.     

Delayed implantation in lactating bank voles, Clethrionomys glareolus.

The time of blastocyst implantation in lactating and non-lactating female bank voles was studied. In primiparous females implantation started 4 days and 9-11 h after mating. A delayed implantation of at least 1 1/2 days was found in lactating, multiparous females when compared to non-lactating, multiparous and primiparous females.     

FEMALES RECEIVE A LIFE-SPAN BENEFIT FROM MALE EJACULATES IN A FIELD CRICKET

Abstract.— Mating has been found to be costly for females of some species because of toxic products that males transfer to females in their seminal fluid. Such mating costs seem paradoxical, particularly for species in which females mate more frequently than is necessary to fertilize their eggs. Indeed, some studies suggest that females may benefit from mating more frequently. The effect of male ejaculates on female life span and lifetime fecundity was experimentally tested in the variable field cricket, Gryllus lineaticeps. In field crickets, females will mate repeatedly with a given male and mate with multiple males. Females that were experimentally mated either repeatedly or multiply lived more than 32% longer than singly mated females. In addition, multiply mated females produced 98% more eggs than singly mated females. Because females received only sperm and seminal fluid from males in the experimental matings, these life‐span and fecundity benefits may result from beneficial seminal fluid products that males transfer to females during mating. Mating benefits rather than mating costs may be common in many animals, particularly in species where female mate choice has a larger effect on male reproductive success than does the outcome of sperm competition.     

Oogenesis and gonad maturation in the copepodCalanus finmarchicus and the prediction of egg production from preserved samples

 Oogenesis and gonad development of Calanus finmarchicus during the winter spring transition in a fjord in Northern Norway were studied. A combination of observations on whole animals (macroscopic), taking advantage of their transparency, and histological sections was used to establish a system of gonad maturation stages, to describe the spawning cycle and to estimate egg production rates from preserved samples. During their development, oocytes change their shape and size, the morphology of the nucleus, and the appearance of the ooplasm. Four oocyte development stages were identified and related to a macroscopic system of four gonad developmental stages (GS) that can be applied to whole stained animals. During gonad development, the macroscopic morphological modifications of the gonads are mainly manifested in an increase in number and size of the oocytes and their distribution in diverticula and oviducts. The maturation processes during the spawning cycle (the period between egg depositions) were described from histological sections of females preserved at regular intervals after egg deposition. The macroscopic GS did not vary during the spawning cycle. This GS was a highly significant indicator for females, which spawned within 24 h after collection at 5°C. Another histological indicator for the last third of the spawning cycle is the appearance of distinct chromosomes, which, however, are only seen in histological sections. For the prediction of egg production rate of a Calanus population, in addition to the number of females spawning, knowledge of clutch size and the interval of clutch deposition is required. Clutch size was determined by counting the number of the oocyte stages to be released during the next spawning event in serial sections of the gonads. There was no significant difference in clutches laid by the females during 5 days before preservation. From the observations it seems that GS 4 predicts females that are ready to spawn within the minimum spawning interval characterisitic for a given temperature. If this holds true, it should be possible to predict in situ egg production rates solely from preserved samples. Received: 18 August 1995/Accepted: 6 January 1996     

Receptivity of female remating and sperm number in the sperm storage organ in the bean bug,Riptortus clavatus (Heteroptera: Alydidae)

This study examines the relationship between the number of sperm in the seminal receptacle (spermatheca) and the receptivity of female remating in the bean bugRiptortus clavatus Thunberg. On the 21 st day after the first mating when receptivity to remating was > 70%, females receptive to remating had significantly fewer sperm ( < 40 on average) in the spermathecae than females reluctant to do (about 150 on average). However, averages of the number of eggs laid by receptive and reluctant females within 21 days were almost same. The proportion of fertilized eggs for receptive females at 15–21 days after copulation was significantly lower than that for reluctant females. Spermatozoa transferred from a male to a female’s spermatheca were detected 5 min after copulation and then increased continuously to about 500 with the first hour. When copulation durations were manipulated artificially, the shorter the copulation period (=females had less sperm in their spermathecae), the higher the remating rate became. Females may perceive the number of sperm in their seminal receptacles and then determine whether they copulate or not. These results support the hypothesis that females mate multiply in order to replenish inadequate sperm supplies to fertilize all eggs produced.     

The effects of primiparity on reproductive performance in the brown bear

We studied the effects of primiparity on litter size, offspring size, and cub loss in brown bears (Ursus arctos) in two study areas (north, south) in Sweden from 1987 to 2006. Sexually selected infanticide (SSI) has been suggested previously as a mortality factor in our study populations. Females in the south became primiparous earlier than females in the north. Primiparous females had significantly smaller litters of cubs than multiparous females. We found no evidence that primiparity was costly in terms of the interlitter interval. Primiparous mothers had a higher probability of cub loss than multiparous mothers. The probability of cub loss was analyzed separately for the pre-mating and the mating season. The probability of cub loss by primiparous females in the pre-mating season increased with both increasing population density and deteriorating food conditions, whereas the probability of cub loss during the mating season decreased with increasing age of primiparity and increased with male turnover (a variable predicting SSI). The temporal patterns of cub loss by primiparous females suggested that the critical times for reproductive success by primiparous females were the pre-mating season (from birth to shortly after leaving the den) and the mating season. Cub loss in these periods was independent and caused by different factors. Cub loss before the mating season seemed to be most influenced by food conditions, whereas that during the mating season appeared to be caused by SSI.