Testis size, sperm characteristics and testosterone concentrations in four species of shrews (Mammalia, Soricidae)

Parapanov, Roumen; Nusslé, Sébastien; Crausaz, Michel; Senn, A.; Hausser, Jacques; Vogel, Peter

doi:10.1016/j.anireprosci.2008.09.013

Cited by 16 publications

(11 citation statements)

References 43 publications

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“…The existence of some receptive females in the summer seems not to be the cause of the peculiar situation we have shown in C. russula , as they appear to be quite exceptional. Rather, it could be related to the fact that males are relatively monogamous, a condition generally associated with the presence of small testes (see Hosken et al, ; Parapanov et al, ), and a reduced spermatogenesis investment would not represent an excessive energy cost if maintained during the non‐breeding season. However, this cannot be the only cause, as data reported by López‐Fuster et al () indicate that males from populations of northern Spain undergo testis regression.…”

Section: Discussionmentioning

confidence: 99%

The testis of greater white‐toothed shrew Crocidura russula in Southern European populations: A case of adaptive lack of seasonal involution?

et al. 2014

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Males of all seasonal breeding mammals undergo circannual periods of testis involution resulting in almost complete ablation of the germinative epithelium. We performed a morphometric, histological, hormonal, and gene-expression study of the testes from winter and summer males of the greater white-toothed shrew, Crocidura russula, in populations of the southeastern Iberian Peninsula. Unexpectedly, we found no significant differences between the two study groups. Surprisingly, female data confirmed a non-breeding period in the summer, evidencing that males retain full testis function even when most females are not receptive. This situation, which has not been described before, does not occur in northern populations of the same species where, in addition, the reproductive cycle is inverted with respect to those in the south, as the non-breeding period occurs in winter instead in summer. Considering that the non-reproductive period shortens at lower latitude locations, we hypothesize that in southern populations the non-breeding period is short enough to make testis regression inefficient in terms of energy savings, because: (1) testes of C. russula are very small, a condition derived from their monogamy that implies low investment in spermatogenesis; and (2) the spermatogenic cycle of this species is slow and long. The inverted seasonal breeding cycle and the lack of seasonal testis regression described here are new adaptive processes that deserve further research, and provide evidence that the genetic and hormonal mechanisms controlling reproduction timing in mammals are more plastic and versatile than initially suspected.

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Section: Discussionmentioning

confidence: 99%

The testis of greater white‐toothed shrew Crocidura russula in Southern European populations: A case of adaptive lack of seasonal involution?

et al. 2014

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“…Whether it can be applied to other taxonomic groups remains to be studied, but circumstantial evidence suggests that a negative relationship between intraspecific sperm length variation and sperm competition risk also exist in mammals [63], e.g. shrews [64], murine rodents [65] and hominids [66].…”

Section: Discussionmentioning

confidence: 99%

Sperm Length Variation as a Predictor of Extrapair Paternity in Passerine Birds

et al. 2010

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BackgroundThe rate of extrapair paternity is a commonly used index for the risk of sperm competition in birds, but paternity data exist for only a few percent of the approximately 10400 extant species. As paternity analyses require extensive field sampling and costly lab work, species coverage in this field will probably not improve much in the foreseeable future. Recent findings from passerine birds, which constitute the largest avian order (∼5 900 species), suggest that sperm phenotypes carry a signature of sperm competition. Here we examine how well standardized measures of sperm length variation can predict the rate of extrapair paternity in passerine birds.Methodology/Principal FindingsWe collected sperm samples from 55 passerine species in Canada and Europe for which extrapair paternity rates were already available from either the same (n = 24) or a different (n = 31) study population. We measured the total length of individual spermatozoa and found that both the coefficient of between-male variation (CVbm) and within-male variation (CVwm) in sperm length were strong predictors of the rate of extrapair paternity, explaining as much as 65% and 58%, respectively, of the variation in extrapair paternity among species. However, only the CVbm predictor was independent of phylogeny, which implies that it can readily be converted into a currency of extrapair paternity without the need for phylogenetic correction.Conclusion/SignificanceWe propose the CVbm index as an alternative measure to extrapair paternity for passerine birds. Given the ease of sperm extraction from male birds in breeding condition, and a modest number of sampled males required for a robust estimate, this new index holds a great potential for mapping the risk of sperm competition across a wide range of passerine birds.

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“…Androgens are shown to suppress the immune function (Folstad and Karter 1992;Hughes and Randolph 2001) or directly increase parasitic loads (Mougeot et al 2005), leading to higher abundance, prevalence and/or species richness of parasites in male hosts Krasnov et al 2005b;Matthee et al 2010; but see Rolff 2002). Larger testes presumably produce more testosterone (Parapanov et al 2009). A larger concentration of testosterone may, in turn, amplify its immunosuppression effect and facilitate the establishment of species-rich parasite assemblages.…”

Section: Testes Size and Parasite Species Richnessmentioning

confidence: 98%

“…Given above mentioned relationships between parasite diversity and host immune defence (Morand and Poulin 2000;Møller and Rozsa 2005;Bordes and Morand 2009b;Š imková et al 2008), richer parasite assemblages are likely be found in host species with larger testes and/or brain. In addition, larger testes are associated with higher testosterone levels (Parapanov et al 2009). An immunosuppressive effect of androgens is often implied for the explanation of characteristic mammalian male-biased parasitism (Zuk and McKean 1996) in terms of, for example, higher parasite species richness in male hosts ).…”

Section: Introductionmentioning

confidence: 97%

Does investment into “expensive” tissue compromise anti-parasitic defence? Testes size, brain size and parasite diversity in rodent hosts

2010

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Species richness of parasite assemblages varies among host species. Earlier studies that searched for host-related determinants of parasite diversity mainly considered host traits that affect the probability of host encounter with parasites, whereas host traits related to defensibility against parasites have rarely been investigated. From the latter perspective, evolutionary investment in "expensive" tissue or organs (like testes or brain) may trade off against energetically costly anti-parasitic defences. If so, richer parasite assemblages are expected in hosts with larger testes and brains. We studied the relationships between testes and brain size and diversity of parasites (fleas, gamasid mites and helminths) in 55 rodent species using a comparative approach and application of two methods, namely the method of independent contrasts and generalized least-squares (GLS) analysis. Both phylogenetically correct methods produced similar results for flea and helminth species richness. Testes size positively correlated with flea and helminth species richness but not gamasid mite species richness. No correlation between brain size and species richness of any parasite group was found by the method of independent contrasts. However, GLS analysis indicated negative correlation between brain size and mite species richness. Our results cast doubt on the validity of the expensive tissue hypothesis, but suggest instead that larger testes are associated with higher parasite diversity via their effect on mobility and/or testosterone-mediated immunosuppression.

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Testis size, sperm characteristics and testosterone concentrations in four species of shrews (Mammalia, Soricidae)

Cited by 16 publications

References 43 publications

The testis of greater white‐toothed shrew Crocidura russula in Southern European populations: A case of adaptive lack of seasonal involution?

The testis of greater white‐toothed shrew Crocidura russula in Southern European populations: A case of adaptive lack of seasonal involution?

Sperm Length Variation as a Predictor of Extrapair Paternity in Passerine Birds

Does investment into “expensive” tissue compromise anti-parasitic defence? Testes size, brain size and parasite diversity in rodent hosts

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