Seasonal patterns of sperm storage in the Yellow-headed Blackbird Xanthocephalus xanthocephalus

The seasonal pattern of sperm storage was examined in a wild population of Yellow-headed Blackbirds Xanthocephalus xanthocephalus by collecting females at eight different stages of their breeding cycle. Sperm storage tubules (SSTs) were present in simiktr numbers throughout all stages of the breeding season, from arrival on the breeding grounds to departure for winter. In contrast, the size of SSTs varied enormously over the season, reaching maximum size just prior to clutch initiation, when SSTs were more than three times the length of those found in post-breeding birds. The amount of sperm stored also varied over the season, in parallel with the growth and regression of SSTs. Sperm were first observed in SSTs approximately 2–5 days before laying and increased rapidly in abundance until clutch initiation. The amount of sperm stored then decreased gradually during the egg-laying period so that by clutch completion approximately 70% of stored sperm had disappeared from the SSTs. The rapid seasonal development and subsequent regression of SSTs in the Yellow-headed Blackbird contrast sharply with the pattern found in domestic poultry, where the imposition of continuous laying regimes has; led to the maintenance of SSTs at maximum size for extended periods of time.     

Trade-off between reproduction and moult – a comparison of three Fennoscandian pied flycatcher populations

Organisms that reproduce at high latitudes are assumed to have evolved several adaptations to the short summer. For birds, and especially for long-distance migrants, there is a time constraint because both reproduction and moult must be completed before autumn migration. It has therefore been assumed that birds at northern latitudes must initiate their moult during reproduction more often than birds at low latitudes. To investigate how passerine birds breeding at different latitudes allocate their time between reproduction and moult, we compared timing of these activities during three consecutive breeding seasons in three widely separated populations of the pied flycatcher Ficedula hypoleuca. Our results show that the frequency of individuals with moult-breeding overlap, and moult initiation in relation to breeding stage, varied considerably among populations and years. In all three populations, female moult initiation was restricted to the late nestling period. The males had a more pronounced moult-breeding overlap than the females, but its duration was similar in all three study areas. Thus, there was no evidence for a more pronounced moult-breeding overlap at high compared with low latitudes. These results suggest that pied flycatchers sometimes accept a moult-breeding overlap, but that the time gained by having too extensive an overlap between reproduction and moult does not outweigh the associated costs. Long-distance migrants breeding at northern latitudes apparently experience a trade-off between reproduction and somatic investment during moult. We therefore suggest that a pronounced moult-breeding overlap is not a typical strategy used by long-distance migrants to adjust to the short breeding season at northern latitudes. Received: 7 May 1998 / Accepted: 24 August 1998     

Extensive Use of Intertidal Habitat by Shorebirds Outside Protected Nesting Areas

Conservation of shorebirds throughout their breeding and migratory ranges has become a priority as shorebird populations decline globally. Along the North Atlantic Coast, management efforts have particularly focused on preserving nesting habitat for piping plovers (Charadrius melodus), which are protected under the Endangered Species Act. It is unclear whether these conservation measures suffice to protect foraging habitat for piping plovers and other shorebirds on stopover during migration along the Atlantic Flyway. To evaluate the extent to which conservation of piping plover nesting areas extends to all habitats used by plovers, and to determine whether these protections also benefited non-breeding migratory shorebirds in the region, we conducted weekly shorebird surveys, recording the number and locations of piping plovers and other species, during northward and southward migration on Fire Island and Westhampton Island, New York, USA, from 2014–2016. We used canonical correspondence analysis (CCA) to assess the degree of spatiotemporal overlap between breeding plovers, foraging plovers, and other migratory shorebirds that temporarily stage at the site. The spatiotemporal distribution of migratory shorebirds matched more closely with piping plovers seen during foraging than piping plovers observed tending nests and engaging in other breeding activities. Migratory shorebirds and foraging piping plovers were more abundant and frequent in wet intertidal zones outside of fenced-off nesting areas, which were not protected under current management regimes. Therefore, additional protection of piping plover foraging habitat could benefit plovers and migratory shorebirds that use similar feeding grounds during stopover on northward and southward migration. © 2020 The Wildlife Society.     

Fat reserves of migrating passerines at arrival on the breeding grounds in Swedish Lapland

Mist-net capture data taken during 6 years (1988–1990 and 1992–1994) of field work were used to describe the arrival sequences and fat loads of nine species of migratory passerines which breed in a near-Arctic environment in Swedish Lapland. Long-distance migrants arrived with significantly larger mean fat reserves than did medium- and short-distance migrants. Long-distance migrants carried fat loads at arrival which corresponded to potential remaining flight distances between 242 and 500 km. When females and males arrived on the breeding grounds simultaneously, females carried significantly larger energy reserves than did males in seven out of nine species. In contrast, when the sexes showed a significant difference in median arrival date (two out of nine species), there was no difference in mean fat load carried into the breeding area. A relationship was found between the migratory habits and foraging ecology of each species and the amount of fat reserves at arrival, suggesting that species-specific migratory distances and feeding habits determine the amount of fat that is needed during the transition period between migration and onset of breeding. The short growing season in the study area restricts the time available for breeding and moult, and large energy reserves at arrival may speed up the breeding schedule to counteract possible time constraints. Overloading at the last stopover site during spring migration may be an adaptation allowing birds to cope with a restricted time frame for breeding and moult at high latitudes.     

Community composition, seasonal dynamics and interspecific correlation of waterbirds in the Qiantangjiang River estuary and Hangzhou Bay

Waterbird surveys were conducted regularly in the Qiantangjiang River estuary and Hangzhou Bay from July 2007 to November 2011. A total of 128 species (nine orders and 18 families) were recorded, including 119 migrants which accounted for 93% of the total species; eleven species were listed as National Protected Species. Inter-specific correlation analysis for 13 shorebird populations and nine duck populations recorded over time found that 21 pairs of shorebirds and 23 pairs of ducks were correlated. By looking at seasonal dynamics and migration patterns we were able to divide the migration process into six stages: (1) late July to late September was the migration peak of shorebirds, which were dominated by Limosa limosa, Calidris ruficollis and Charadrius mongolus. (2) Early October to mid-December was the migration peak of wintering migrants of shorebirds and ducks, which were the first two large groups in our study areas. (3) Late December to mid-February was the wintering period of migration waterbirds. (4) Late February to late March was the peak migration of ducks and the winter migrants of shorebirds dominated by Calidris alpina. (5) Early April to mid-May was the migration peak of passage migrants such as, Calidris ruficollis, Calidris acuminate and Limosa limosa but the population size of shorebird winter migrants dominated by Calidris alpine was still larger than the former. (6) Late May to mid-July was the breeding season of all egrets, summer migrants of gulls and several species of shorebirds. Our surveys show that interaction among species is possibly an important determinant of community composition of shorebirds and wintering ducks during the migration season. It may be the geographical position and community composition of migrant shorebirds across Hangzhou Bay that mean during the northward migration there are far more shorebirds than during the southward migration.     

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.     

Young and female‐biased irruptions in pygmy owls Glaucidium passerinum in southern Finland

Irruptive migrants often show biased sex and age ratio, and typically young females are the most abundant class participating in irruptions. Several hypotheses have been proposed to explain differential migration in birds. We examined these hypotheses in a sexually size‐dimorphic species (females being larger than males), the pygmy owl Glaucidium passerinum, whose migration behaviour has also been poorly documented. Migration data were collected at the Hanko Bird Observatory, SW Finland during 1979–2010. Pygmy owls showed large fluctuations in migration numbers between years. Most of the migrants were young birds and females migrated in larger numbers than males. Results support the ‘territory defence hypothesis’ since males showed weaker tendency to migrate despite the smaller body size, but the ‘dominance hypothesis’ was also supported (subordinate young outnumber dominant adults in migration numbers). Findings support the idea that in owl species, which are dependent on nesting cavities, males show lower migration behaviour than females, whereas the pattern is opposite in species which normally breed outside cavities. In addition, adults migrated later than young, likely because they need to moult remiges before departure. Early hatched young also migrated earlier than late hatched young, suggesting that more dominant young migrate first.     

Basal metabolic rate and energetic cost of thermoregulation among migratory and resident blue tits

Metabolic rates may be informative of adaptations to migration or wintering at high latitudes and may therefore be particularly interesting in partial migrants requiring adaptations to both migration and residency. To study the extent of physiological adaptations in migratory and resident blue tits Cyanistes caeruleus during the period of autumn migration in southern Sweden, we measured basal metabolic rate (BMR) and cost of thermoregulation at 0°C (CTR0). In contrast to other migrants en route, migratory blue tits had lower BMR than residents. As migratory blue tits travel extraordinarily slowly on autumn migration and residents suffer from harsher climate and severe competition, residents may need dynamic adjustments that involve larger metabolic costs than migrants. Resident males had lower CTR0 than migrants and resident females. Resident males are socially dominant, which suggests that they have priority of access to food sources during summer and early autumn. They also spend more time on moult, which would give them the time and energy needed for molting into a plumage of higher insulation quality than is possible for migrants and resident females.     

Male mating behavior and ejaculate expenditure under sperm competition risk in the eastern mosquitofish

Theory predicts that males should tailor the size of their ejaculatesaccording to temporal changes in the risk of sperm competition.Specifically, males are predicted to allocate more sperm toeach mating event with increasing risk (i.e., the probabilitythat the sperm from two males will compete for fertilization).We tested this hypothesis by using the eastern mosquitofish,a freshwater species of fish exhibiting a coercive mating systemand internal fertilization. We manipulated the perception ofsperm competition risk by adjusting the sex ratio under whichmales were maintained over 8 days. Males were housed eitherwith three females and one male (simulating high sperm competitionrisk) or with four females (low risk). After the treatment,we presented each test male individually to an unfamiliar male-deprivedfemale for 30 minutes and observed his mating behavior. We thenartificially stripped the test males of sperm and recoveredthe ejaculates from the females. Our results revealed that malesin the high-risk group performed higher levels of mating activityand sperm expenditure (i.e., used up more of their sperm reserves)than did low-risk males. A control experiment, in which testmales were treated but did not participate in the mating trials,revealed no significant difference in the number of sperm strippedfrom high- and low-risk males, indicating that sperm productionwas not affected by the treatment. We did not detect a differencein the number of sperm retrieved from females among the groups,raising the possibility that some sperm are lost during matingactivity, either through ejaculation with incomplete or interruptedpenetration, or via female ejection.     

Ecological factors associated with the breeding and migratory phenology of high-latitude breeding western sandpipers

Environmental conditions influence the breeding and migratory patterns of many avian species and may have particularly dramatic effects on long-distance migrants that breed at northern latitudes. Environment, however, is only one of the ecological variables affecting avian phenology, and recent work shows that migration tactics may be strongly affected by changes in predator populations. We used long-term data from 1978 to 2000 to examine the interactions between snowmelt in western Alaska in relation to the breeding or migration phenologies of small shorebirds and their raptor predators. Although the sandpipers’ time of arrival at Alaskan breeding sites corresponded with mean snowmelt, late snowmelts did delay breeding. These delays, however, did not persist to southward migration through British Columbia, likely due to the birds’ ability to compensate for variance in the length of the breeding season. Raptor phenology at an early stopover site in British Columbia was strongly related to snowmelt, so that in years of early snowmelt falcons appeared earlier during the sandpipers’ southbound migration. These differential effects indicate that earlier snowmelt due to climate change may alter the ecological dynamics of the predator–prey system.     

North Atlantic Oscillation and timing of spring migration in birds

Migrant birds have been trapped on the island of Helgoland (southeastern North Sea) since 1909, with methods and sampling effort remaining unchanged throughout the last four decades. In 12 short/medium-distance migrants and 12 long-distance migrants (23 passerines plus the European woodcock) sample sizes were sufficient to calculate mean spring passage (msp) times and to relate these to climate change. All but one species, passing Helgoland en route to their breeding areas (mainly in Scandinavia), show a trend towards earlier msp-time, which is significant in 7 short/medium-distance migrants and 10 long-distance migrants. The msp-times advanced by 0.05-0.28 days per year, short/medium-distance migrants not differing from long-distance migrants. In 23 out of the 24 species, earlier msp-times coincide with local warmer msp-temperatures (significantly in 11 and 7 species of the two groups, respectively). Even more striking is the relation to a large-scale phenomenon, the North Atlantic Oscillation (NAO), during the last four decades. Again, in 23 out of the 24 species, an earlier msp-time coincides with higher NAO indices (significantly in 9 and 12 species, respectively). The NAO index can also explain differences and similarities in spring migration strategies, as well as migration routes within Europe.     

Differences in sperm migration through cervical mucus in vitro relates to sperm colonization of the oviduct and fertilizing ability in goats

Sperm migration in estrous cervical mucus can be used to measure the ability of spermatozoa to migrate through the genital tract. The relationship of this test with the sperm colonization of the isthmus, and its impact on fertility has not been evaluated in goats. Our objectives were to determine the differences among spermatozoa of different bucks in their ability to penetrate homologous cervical mucus in vitro and to determine the relationship between sperm displacement through cervical mucus and the ability of spermatozoa to colonize the oviduct and penetrate IVM oocytes, in vivo. Sperm migration in cervical mucus was assessed in flat capillary tubes with a phase contrast microscope. In the first experiment, fresh semen was used to establish differences between males in the ability of their spermatozoa to migrate in cervical mucus. In the second experiment, goats in estrus were inseminated with fresh spermatozoa from males with significant differences in mucus migration ability, and sperm numbers were evaluated at the UTJ. In the third experiment, the fertilization efficiency of IVM oocytes transferred to the oviduct of estrous females inseminated with semen from the same males as earlier, was used to assess the relationship between the mucus migration test and the in vivo fertilization performance of their spermatozoa. Spermatozoa from different males varies significantly in sperm migration efficiency in cervical mucus (15.5a +/- 1.2; 14.9a +/- 1.4; 17.5ab +/- 1.2; 17.0ab +/- 1.5; 19.7b +/- 1.2; 20.1b +/- 1.4 mm; media +/- S.E.M. for males A-F, respectively, P < 0.05). Spermatozoa from males with different mucus migration efficiency values produced different sperm populations at the oviduct reservoir of inseminated females (1,233 +/- 92.3 versus 28.8 +/- 17.0 spermatozoa of males with high and low relative migration efficiency, respectively, P < 0.02). Spermatozoa from males with different mucus migration efficiency values have different fertilization rates of IVM oocytes transferred to oviduct (47/96 (49.0%) versus 25/91 (27.5%) for males with high and low relative migration efficiency, respectively, P < 0.05). Cumulative results suggest that sperm migration in cervical mucus is related to the ability of spermatozoa to colonize the oviduct and to fertilize matured oocytes in vivo.     

Numbers and size of sperm storage tubules and the duration of sperm storage in birds: a comparative study

Estimates of the numbers of sperm storage tubules (SSTs) in the utero-vaginal junction of 11 bird species are presented. Numbers of SSTs varied by a factor of 40 between species, and ranged from 500 to 20000. Body mass accounted for over 50% of the variation in SST mumbers. SST length was positively correlated with the length of spermatozoa across species. The duration of sperm storage was not correlated with the number of SSTs or the volume of sperm storage tissue. However, the number of 'active' SSTs appears to vary between species and it was not possible to make allowance for this. Sperm storage duration was weakly, positively correlated wth clutch size, but showed a significant positive relationship with the number of days over which laying occurred. The number of SSTs was also positively correlated with the number of sperm per ejaculate. The best predictor of sperm storage duration was a multiple regression equation using the spread of laying and the length of sperm storage tubules. The duration of sperm storage in birds which remain together during the pre-laying period is such that a single insemination immediately before the start of laying could fertilize the entire clutch.     

Melanin-based Feather Colour and Moulting Latitude in a Migratory Songbird

Melanins are common pigments used for colouration in animal tissue and recent evidence suggests that they may be condition-dependent signals used in mate choice. We examined the hypothesis that individuals moulting during migration produce relatively dull feathers compared to individuals moulting on the breeding grounds prior to migration because of the costs associated with overlapping these two activities. We estimated both the colour and moulting latitude of melanin-based feathers in barn swallows ( Hirundo rustica ). Moulting latitude was inferred from stable-hydrogen isotope (δD) values of individuals that were known to have bred at the same site the previous year. Contrary to expectations, δD values in feathers suggested that most, if not all, individuals moulted their feathers south of the breeding grounds. Furthermore, we found that males moulting at southern latitudes tended to produce darker, more rufous coloured throat feathers compared to males moulting at more northern latitudes, closer to the breeding grounds. However, we found no such relationship in females. Males could face a trade-off between growing new but relatively dull feathers before or just after the commencement of migration versus waiting to grow more rufous coloured feathers well into fall migration or on the wintering grounds. We suggest that this trade-off could produce an honest signal of male quality if only high quality males can afford to migrate large distances on feathers that are greater than a year old.     

Breeding plumage honestly signals likelihood of tapeworm infestation in females of a long-distance migrating shorebird, the bar-tailed godwit

The indicator mechanism for sexual selection proposed by Hamilton and Zuk (i.e. that sexually selected ornaments signal parasite resistance) has received rather little observational support, and none in the case of long-distance migrant birds. Here we present a test by examining the association between helminth infestations and breeding plumage quality in bar-tailed godwits Limosa lapponica taymyrensis during their spring staging period in the Wadden Sea, The Netherlands. After a non-stop flight from West Africa, these shorebirds refuel in the Wadden Sea in preparation for a second flight to the central Siberian Arctic breeding grounds. Earlier studies have shown that only relatively heavy and well ornamented birds carry out a "top-up" moult during stopover, in which part of the contour feathers recently grown in West Africa are replaced by even fresher ones. Active body moult was therefore taken as the primary indicator of ornament quality. Of 78 birds collected between 1992 and 1997, 42% carried helminths, including four species of digenean trematodes (flukes), three species of cestodes (tapeworms) and an acanthocephalan (spiny-headed worm). Faecal samples examined for helminth eggs in another 92 birds in 1998 and 2000 showed similar rates of infestation. Actively moulting bar-tailed godwits were confirmed to be heavier and to show more extensive breeding plumage than non-moulting birds. In females, but not in males, active moult was associated with fewer cestodes and acanthocephalans. Also, breeding plumage and presence of cestodes were negatively associated in females. We argue that the quality of the breeding plumage reliably indicates parasite resistance in female godwits. The repeatability of plumage scores of females between years is consistent with such resistance having a heritable component. In contrast, male ornaments may demonstrate other qualities, e.g. an ability to combine adequate fuelling and flight performances with moult during the time-stress of migration.     

Why fly the extra mile? Latitudinal trend in migratory fuel deposition rate as driver of trans‐equatorial long‐distance migration

Trans‐equatorial long‐distance migrations of high‐latitude breeding animals have been attributed to narrow ecological niche widths. We suggest an alternative hypothesis postulating that trans‐equatorial migrations result from a possible increase in the rate at which body stores to fuel migration are deposited with absolute latitude; that is, longer, migrations away from the breeding grounds surpassing the equator may actually enhance fueling rates on the nonbreeding grounds and therewith the chance of a successful, speedy and timely migration back to the breeding grounds. To this end, we first sought to confirm the existence of a latitudinal trend in fuel deposition rate in a global data set of free‐living migratory shorebirds and investigated the potential factors causing this trend. We next tested two predictions on how this trend is expected to impact the migratory itineraries on northward migration under the time‐minimization hypothesis, using 56 tracks of high‐latitude breeding shorebirds migrating along the East Asian‐Australasian Flyway. We found a strong positive effect of latitude on fuel deposition rate, which most likely relates to latitudinal variations in primary productivity and available daily foraging time. We next confirmed the resulting predictions that (1) when flying from a stopover site toward the equator, migrants use long jumps that will take them to an equivalent or higher latitude at the opposite hemisphere; and (2) that from here onward, migrants will use small steps, basically fueling only enough to make it to the next suitable staging site. These findings may explain why migrants migrate “the extra mile” across the equator during the nonbreeding season in search of better fueling conditions, ultimately providing secure and fast return migrations to the breeding grounds in the opposite hemisphere.     

Butterflies tailor their ejaculate in response to sperm competition risk and intensity

Males of many insects eclose with their entire lifetime sperm supply and have to allocate their ejaculates at mating prudently. In polyandrous species, ejaculates of rival males overlap, creating sperm competition. Recent models suggest that males should increase their ejaculate expenditure when experiencing a high risk of sperm competition. Ejaculate expenditure is also predicted to vary in relation to sperm competition intensity. During high intensity, where several ejaculates compete for fertilization of the female''s eggs, ejaculate expenditure is expected to be reduced. This is because there are diminishing returns of providing more sperm. Additionally, sperm numbers will depend on males'' ability to assess female mating status. We investigate ejaculate allocation in the polyandrous small white butterfly Pieris rapae (Lepidoptera). Males have previously been found to ejaculate more sperm on their second mating when experiencing increased risk of sperm competition. Here we show that males also adjust the number of sperm ejaculated in relation to direct sperm competition. Mated males provide more sperm to females previously mated with mated males (i.e. when competing with many sperm) than to females previously mated to virgin males (competing with few sperm). Virgin males, on the other hand, do not adjust their ejaculate in relation to female mating history, but provide heavier females with more sperm. Although virgin males induce longer non-receptive periods in females than mated males, heavier females remate sooner. Virgin males may be responding to the higher risk of sperm competition by providing more sperm to heavier females. It is clear from this study that males are sensitive to factors affecting sperm competition risk, tailoring their ejaculates as predicted by recent theoretical models.     

Do the high energy lifestyles of shorebirds result in high maximal metabolic rates? Basal and maximal metabolic rates in least and pectoral sandpipers during migration

Shorebirds have high resting and field metabolic rates relative to many other bird groups, and this is posited to be related to their high‐energy lifestyle. Maximum metabolic outputs for cold or exercise are also often high for bird groups with energetically demanding lifestyles. Moreover, shorebirds demonstrate flexible basal and maximal metabolic rates, which vary with changing energy demands throughout the annual cycle. Consequently, shorebirds might be expected to have high maximum metabolic rates, especially during migration periods. We captured least Calidris minutilla and pectoral C. melanotos sandpipers during spring and fall migration in southeastern South Dakota and measured maximal exercise metabolic rate (MMR; least sandpipers only), summit metabolic rate (M_sum, maximal cold‐induced metabolic rate) and basal metabolic rate (BMR, minimum maintenance metabolic rate) with open‐circuit respirometry. BMR for both least and pectoral sandpipers exceeded allometric predictions by 3–14%, similar to other shorebirds, but M_sum and MMR for both species were either similar to or lower than allometric predictions, suggesting that the elevated BMR in shorebirds does not extend to maximal metabolic capacities. Old World shorebirds show the highest BMR during the annual cycle on the Arctic breeding grounds. Similarly, least sandpiper BMR during migration was lower than on the Arctic breeding grounds, but this was not the case for pectoral sandpipers, so our data only partially support the idea of similar seasonal patterns of BMR variation in New World and Old World shorebirds. We found no correlations of BMR with either M_sum or MMR for either raw or mass‐independent data, suggesting that basal and maximum aerobic metabolic rates are modulated independently in these species.     

Correlates of timing of spring migration in birds: a comparative study of trans-Saharan migrants

The evolution of migratory strategies in birds is likely to have been influenced by ecological as well as socio-sexual factors in both wintering and breeding areas. In this comparative study, we analysed timing of spring passage of 38 long-distance migratory bird species that winter south of the Sahara desert and breed in Europe, in relation to wintering and breeding latitudes, moult strategy, nesting site (open vs. cavity), and sexual dimorphism in size and coloration, which may reflect intensity of sexual selection. We employed a large data set consisting of more than 190 000 individuals ringed during spring migration in the Mediterranean Sea. We found that the species that migrated earlier were those wintering farther north, nesting in cavities and showing the largest degree of sexual size dimorphism (SSD). However, sexual dichromatism was not related to migration date. Among passerine species, moulting wing-feathers in Africa delayed migration. We found no support for the energetic constraint hypothesis, which proposes that early arrival selects for large male size, since early arriving species were not larger than late arriving ones. Thus, the observed associations suggest that variation in migration schedules at the interspecific level may have evolved in relation to ecological factors and SSD, possibly reflecting the intensity of mating competition.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 199–210.     

Female sperm storage in amphibians.

The three orders of extant amphibians are Gymnophiona, Anura, and Urodela. Although all gymnophionans apparently have internal fertilization and many are viviparous, female sperm storage is unknown. Internal fertilization has convergently evolved in a few anurans, but females of just one species, Ascaphus truei, are known to possess oviductal sperm storage tubules (SSTs). The SSTs of A. truei are similar anatomically to such glands in squamate reptiles. This similarity is convergence due to similar functional adaptations and/or internal design constraints. In salamanders and newts (Urodela), absence of sperm storage in females is the ancestral condition (three families). In the derived condition, sperm storage occurs in cloacal glands called spermathecae, and their possession is a synapomorphy for females in the suborder Salamandroidea (seven families). Salamandroids are the only vertebrates with cloacal sperm storage glands. In this paper, a phenetic analysis of variation in spermathecal characters reveals patterns of convergence in certain spermathecal characters in unrelated taxa that breed in similar habitats. In the family Salamandridae, a role in sperm nutrition for the spermathecal epithelium is questioned, and the widespread occurrence of spermiophagy is related to other reproductive strategies. I propose how the packaging of sperm in structurally different types of spermathecae may influence male paternity.