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51.
Inbreeding depression and its consequences for mate choice have been extensively studied in free-living animals. However, very little is known about its significance for parasites, although it is well recognized that the mating systems of parasites can have important implications for their epidemiology and evolution. In this article, we show that the cestode Schistocephalus solidus shows incestuous mate preference despite evidence for very strong inbreeding depression. When given the simultaneous choice between mating with a sibling and an unrelated partner, on average, the cestode preferred its sibling. To explain this surprising result, we present three hypotheses that suggest different benefits to fitness of incestuous mating, which could, alone or in concert, outweigh the cost of inbreeding depression. 相似文献
52.
Most sex allocation theory is based on the relationship between the resource investment into male and female reproduction and the consequent fitness returns (often called fitness-gain curves). Here we investigate the effects of resource availability on the sex allocation of a simultaneously hermaphroditic animal, the free-living flatworm Macrostomum lignano. We kept the worms under different resource levels and determined the size of their testes and ovaries over a period of time. At higher resource levels, worms allocated relatively more into the female function, suggesting a saturating male fitness-gain curve for this species. A large part of the observed effect was due to a correlated increase in body size, showing size-dependent sex allocation in M. lignano. However, a significant part of the overall effect was independent of body size, and therefore likely due to the differences in resource availability. Moreover, in accordance with a saturating male fitness-gain curve, the worms developed the male gonads first. As the group size was kept constant, our results contrast with expectations from sex allocation models that deal with local mate competition alone, and with previous experiments that test these models. 相似文献
53.
Abd El-Halim A. Saad Fawzy M. A. Ragab Hesham M. Abdel Fatah Nevine K. Ibrahim 《Molluscan research.》2019,39(1):82-88
Controlling the snail intermediate host of schistosomiasis is one of the strategies used to reduce disease incidence. In this study screening tests were carried out on the action of dried powder of eight algal species against Biomphalaria alexandrina snails. The most effective powders were from Dictyota dichotoma and Cystoseira barbata with LC50 values of 560 and 2200?ppm, respectively. Prolonged exposure to sublethal concentrations of these two powders caused adverse effects on snails' reproduction especially at LC25. Hatchability of exposed eggs was lowest at LC25 of C. barbata, and LC15 of D. dichotoma. The most pronounced effects on the hermaphrodite gland of snails were caused by high concentrations of both algal suspensions, where ova were either degenerated or deformed and there were detrimental effects on all spermatogenesis stages. The electrophoretic separation of haemolymph proteins showed that the concentration with most effect was the LC15 for both tested algae as they resulted in more bands than the control and also an elevation in total protein content. 相似文献
54.
Benjamin Pélissié Philippe Jarne Violette Sarda Patrice David 《Evolution; international journal of organic evolution》2014,68(5):1320-1331
Sexual selection operates on a sequence of events, from mating to offspring production. Which stages in this sequence undergo stronger selection, especially the relative importance of pre‐ versus postcopulatory processes, are intensely debated issues. Unequal siring success among mates of polyandrous females is classically taken as evidence for a large contribution of postcopulatory processes to the variance in male reproductive success (var(RSm)). However, paternity skews also depend on the timing and number of copulations, a source of variation that should be considered precopulatory rather than postcopulatory. We develop a method for decomposing var(RSm) accounting for copulatory activity and apply it to experimental mating groups of the snail Physa acuta. In our experiment, 40% of var(RSm) emerges at the precopulatory stage, only half of which depends on variation in mating success (number of partners). Ignoring copulation characteristics can therefore lead to severe underestimation of precopulatory sexual selection. Moreover, although only 36% of var(RSm) arises at the postcopulatory stage, this is when sexual selection on body weight mostly occurs. Finally, trade‐offs were detected between different components of precopulatory success, whereas pre‐ and postcopulatory success appear independent. Our study opens the way to a detailed quantitative understanding of sexual selection in polyandrous species. 相似文献
55.
Imants G. Priede Karen J. Osborn Andrey V. Gebruk Dan Jones David Shale Antonina Rogacheva Nicholas D. Holland 《Invertebrate Biology》2012,131(3):244-257
Enteropneusts in the family Torquaratoridae were imaged using still and video cameras in the deep North Atlantic and then collected by remotely operated vehicles. From this material, we describe Yoda purpurata n. gen, n. sp., Tergivelum cinnabarinum n. sp., and Allapasus isidis n. sp. Individuals of the first two species were browsing completely exposed on the sea floor, whereas the specimen of the last species was encountered floating ~1 m above the sea floor. Living specimens of Y. purpurata were 12–19 cm long and had a dark reddish‐purple proboscis, collar, and genital wings (folded dorsally over the anterior region of the trunk). Members of this species were hermaphrodites (the first ever discovered in the phylum Hemichordata), with numerous separate testes and ovaries in the genital wings. Living specimens of T. cinnabarinum were 12–26 cm long and had a cinnabar‐colored proboscis, collar, and back veils (arising from the anterior region of the trunk); sexes were separate, and body shape and internal morphology closely resemble those of its brown congener, T. baldwinae, from the eastern Pacific. The only specimen of A. isidis collected was a male 13 cm long and pale yellow when alive. Its body shape was proportionally shorter and broader than that of its orange congener, A. aurantiacus, from the eastern Pacific, but the internal anatomy of the two species is virtually identical. [Correction made after online publication August 21, 2012 to correct species name in preceding sentence.] 相似文献
56.
Evolutionary links between reproductive morphology, ecology and mating behavior in opisthobranch gastropods 总被引:2,自引:0,他引:2
Anthes N Schulenburg H Michiels NK 《Evolution; international journal of organic evolution》2008,62(4):900-916
Sexual coevolution in morphological and behavioral traits has rarely been studied. Using phylogenetic analyses, we explore relationships between sexual characters based on a new molecular phylogeny of 33 opisthobranch taxa (Aglajidae and Gastropteridae). Our measurements of these simultaneous hermaphrodites include male and female reproductive anatomy, mating behavior, and spatial gregariousness. After phylogenetic correction, we found evidence for correlated evolution between male and female reproductive organs such as the size of the seminal fluid producing prostate gland and that of the sperm digesting bursa copulatrix. Our findings suggest that reproductive trait variation is mediated by sexual coevolution, where putatively manipulative male organs evolved in association with female organs involved in sperm selection. Furthermore, low gregariousness was associated with long, reciprocal copulations. We interpret this result as an adaptation to infrequent mate encounters, where it pays to mate longer with and presumably transfer more sperm to a rare partner. Several complex reproductive traits were repeatedly gained or lost across our phylogeny. This pattern is consistent with a scenario in which sexual selection generates dynamic coevolutionary cycles similar to those expected under sexual antagonism. We finally outline approaches for experimentally assessing the proposed functional links that underlie the evolutionary correlations revealed by our study. 相似文献
57.
Sperm length and quality in sperm-dependent parthenogens 总被引:1,自引:0,他引:1
THOMAS G. D'SOUZA VERA BELLENHAUS RAMONA WESSELMANN NICO K. MICHIELS 《Biological journal of the Linnean Society. Linnean Society of London》2008,93(1):81-87
Is the male function of parthenogenetic hermaphrodites a historic remnant or an adaptive investment? In the first case, one would expect the male function to be ‘degraded’ and, in the second case, fully functional, despite being reduced. To answer this question, we investigated sperm morphology and quality in the hermaphroditic planarian Schmidtea polychroa. Parthenogenetic forms of this species are sperm‐dependent and require allosperm to trigger embryogenesis. Although there is generally no genetic paternal contribution, occasional fertilization of parthenogenetic eggs has been reported, leading to genetic changes in an otherwise apomictic lineage (‘occasional sex’). Comparing two locations, one with pure clonality and one with occasional sexuality, revealed substantial differences in both sperm length and fertility: Occasional sex appears to be coupled with longer sperm and higher sperm quality. We discuss the implications of these results for the maintenance of the male function in sperm‐dependent parthenogens. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93 , 81–87. 相似文献
58.
Angus Davison Christopher M. Wade Peter B. Mordan Satoshi Chiba 《Journal of Zoology》2005,267(4):329-338
59.
The size-dependent sex allocation model predicts that the relative resource allocation to female function often increases
with plant size in animal-pollinated plants. If size effects on reproductive success vary depending on the environmental conditions,
however, the size dependency may differ among populations. We tried to detect site-specific variation in size-dependent sex
allocation of a monocarpic hermaphrodite with reference to light availability. Multiple flowers and fruits were sampled from
the individuals of Cardiocrinum cordatum, a monocarpic understory herb, and pollen, ovule and seed production were measured with reference to the plant size in two
populations. Furthermore, frequency and foraging behavior of pollinator visitation was observed. Ovule production per flower
increased with plant size in both populations, while pollen production per flower increased with size only in the population
under sparse canopy. Therefore, proportional allocation to male function decreased with plant size in the population under
closed canopy, but did not change in the population under sparse canopy. Pollinators usually visited only one flower per plant,
indicating the negligible geitonogamous pollination in this species. Although seed production under closed canopy was lower
than that under sparse canopy, seed-set rate per flower and seed mass per fruit were independent of plant size in either of
the populations. Size-dependent sex allocation in this species was site-specific, suggesting that not only resource storage
before reproduction (i.e., plant size) but also resource availability of environment throughout the reproductive process (i.e.,
light availability) affect reproductive performance in this species. 相似文献
60.
We isolated 20 trinucleotide microsatellites from two African tree species: Sorindeia madagascariensis (nine microsatellites) and Leptonychia usambarensis (11 microsatellites). Number of alleles ranged from three to seven in Sorindeia and two to 10 in Leptonychia. Observed heterozygosity ranged from 0.025 to 0.829 for Sorindeia and from 0.226 to 0.933 for Leptonychia. Two loci from each species departed from Hardy-Weinberg equilibrium. These microsatellite markers will be used to study how forest fragmentation affects pollination and seed dispersal processes of these tree species. 相似文献