Moderate heritability and low evolvability of sperm morphology in a species with high risk of sperm competition, the collared flycatcher Ficedula albicollis

Abstract

Spermatozoa represent the morphologically most diverse type of animal cells and show remarkable variation in size across and also within species. To understand the evolution of this diversity, it is important to reveal to what degree this variation is genetic or environmental in origin and whether this depends on species’ life histories. Here we applied quantitative genetic methods to a pedigreed multigenerational data set of the collared flycatcher Ficedula albicollis, a passerine bird with high levels of extra‐pair paternity, to partition genetic and environmental sources of phenotypic variation in sperm dimensions for the first time in a natural population. Narrow‐sense heritability (h2) of total sperm length amounted to 0.44 ± 0.14 SE, whereas the corresponding figure for evolvability (estimated as coefficient of additive genetic variation, CVa) was 0.02 ± 0.003 SE. We also found an increase in total sperm length within individual males between the arrival and nestling period. This seasonal variation may reflect constraints in the production of fully elongated spermatozoa shortly after arrival at the breeding grounds. There was no evidence of an effect of male age on sperm dimensions. In many previous studies on laboratory populations of several insect, mammal and avian species, heritabilities of sperm morphology were higher, whereas evolvabilities were similar. Explanations for the differences in heritability may include variation in the environment (laboratory vs. wild), intensity of sexual selection via sperm competition (high vs. low) and genetic architecture that involves unusual linkage disequilibrium coupled with overdominance in one of the studied species.

Sperm Morphology and Male Age in Black-Throated Blue Warblers, an Ecological Model System

“…Furthermore, repeated samples across years of the same individuals show high repeatability in total sperm length, suggesting that between-season changes in sperm morphology within an individual are limited [23,31,42,45,46]. Small within-season changes in morphology, in contrast, appear to be relatively common, occurring in most of the species studied [31,42,43,46] (but see [45]). Older male black-throated blue warblers are more likely to obtain and defend territories with high quality nesting and foraging habitat [47], suggesting that, if they therefore have higher body condition (not assessed in this study), body condition could mediate the greater sperm length observed in older birds.…”

“…In the other passerine birds that have been tested, sperm morphology does not differ between young and old males [40][41][42][43][44]. Furthermore, repeated samples across years of the same individuals show high repeatability in total sperm length, suggesting that between-season changes in sperm morphology within an individual are limited [23,31,42,45,46].…”

“…In the other passerine birds that have been tested, sperm morphology does not differ between young and old males [ 40 , 41 , 42 , 43 , 44 ]. Furthermore, repeated samples across years of the same individuals show high repeatability in total sperm length, suggesting that between-season changes in sperm morphology within an individual are limited [ 23 , 31 , 42 , 45 , 46 ]. Small within-season changes in morphology, in contrast, appear to be relatively common, occurring in most of the species studied [ 31 , 42 , 43 , 46 ] (but see [ 45 ]).…”

Longer Sperm Swim More Slowly in the Canary Islands Chiffchaff

“…Sperm measures vary across the breeding season in some species [64][65][66][67][68] but not all (e.g., [53]). However, our sampling scheme did not allow us to assess or control for such effects here.…”

Sperm velocity in a promiscuous bird across experimental media of different viscosities

“…While there is a growing body of evidence indicating taxonomically widespread phenotypic plasticity in sperm morphology (e.g. [22][23][24]), relatively few studies have addressed plasticity in sperm behaviour. In fish, for example, males were found to produce slower sperm when experimentally promoted to higher ranks in social dominance hierarchies [25] or males responded to perceived sperm competition intensity by producing longer lived [26] or faster sperm [27].…”