Who's My Daddy? Considerations for the influence of sexual selection on multiple paternity in elasmobranch mating systems

Abstract

Polyandry resulting in multiply‐sired litters has been documented in the majority of elasmobranch species examined to date. Although commonly observed, reasons for this mating system remain relatively obscure, especially in batoids. The round stingray (Urobatis halleri) is an abundant, well‐studied elasmobranch distributed throughout the northeastern Pacific that we used to explore hypotheses regarding multiple paternity in elasmobranchs. Twenty mid‐ to late‐term pregnant females were sampled off the coast of southern California and their litters analyzed for the occurrence of multiple paternity using five nuclear microsatellite loci. In addition, embryo sizes and their position within the female reproductive system (i.e., right or left uterus) were recorded and used to make inferences for patterns of ovulation. Multiple paternity was observed in 90% of litters and male reproductive success within litters was relatively even among sires. High variability in testes mass was observed suggesting that sperm competition is high in this species, although male reproductive success per litter appeared to be relatively even. Using embryo size as a proxy for fertilization, females were found to exhibit a variety of ovulation patterns that could function to limit a male's access to eggs and possibly promote high rates of multiple paternity. Our study highlights that elasmobranch mating systems may be more varied and complex than presumed and further investigation is warranted.

An inconvenient tooth: Evaluating female choice in multiple paternity using an evolutionarily and ecologically important vertebrate clade

“…Males' perception of their degree of intraspecific competition is often inferred through reproductive morphometrics in a population, specifically comparing relative testes mass as a proxy for sperm production capability (Kenagy & Trombulak, 1986; Moller & Briskie, 1995; Stockley et al, 1997). In round stingrays, high variation in testes mass suggests that males perceive their degree of intrasexual competition to be high, which is likely considering the high density of stingrays in sampling locations (Lyons et al, 2017). In small‐spotted catsharks, other male reproductive tract morphometrics (epididymis and seminal vesicle diameter, clasper length, testes mass) are significantly larger in one population, which authors attribute to possible differences in sperm competition (Finotto et al, 2015).…”

“…In this scenario sperm from individual males only gain access during specific ovulation windows, leaving subsequent ovulations open to other males. This has been hypothesized to occur in round stingrays where examination of sireship placement of embryos in the right and left uteri indicated that females may cryptically alter ovulation patterns to produce more evenly skewed litters (Lyons et al, 2017). Other species, such as nurse sharks, have protracted ovulation windows where females release eggs over the course of several weeks (Castro, 2000).…”

Legacy polychlorinated biphenyl contamination impairs male embryonic development in an elasmobranch with matrotrophic histotrophy, the round stingray (Urobatis halleri)

“…PCBs are known to have estrogenic as well as antiestrogenic endocrine‐disrupting effects depending on model and factors tested (Hany et al ; Kaya et al ), which could contribute to this negative effect on male embryonic growth. Small size in early life could have lasting negative effects on male fitness as male to male competition is high in mainland round stingrays (Lyons et al ).…”

Sperm motility in ocellate river stingrays: evidence for post‐testicular sperm maturation and capacitation in Chondrichthyes

“…b) and hence increased sperm production would be beneficial for fertilization success. Polyandry resulting in multiply‐sired litters is well confirmed for Chondrichthyes (Lyons et al ., ) and therefore effective and efficient sperm production is probably associated with the risk of sperm competition.…”