REPLICATED ORIGIN OF FEMALE-BIASED ADULT SEX RATIO IN INTRODUCED POPULATIONS OF THE TRINIDADIAN GUPPY (POECILIA RETICULATA)

Abstract

There are many theoretical and empirical studies explaining variation in offspring sex ratio but relatively few that explain variation in adult sex ratio. Adult sex ratios are important because biased sex ratios can be a driver of sexual selection and will reduce effective population size, affecting population persistence and shapes how populations respond to natural selection. Previous work on guppies (Poecilia reticulata) gives mixed results, usually showing a female-biased adult sex ratio. However, a detailed analysis showed that this bias varied dramatically throughout a year and with no consistent sex bias. We used a mark-recapture approach to examine the origin and consistency of female-biased sex ratio in four replicated introductions. We show that femalebiased sex ratio arises predictably and is a consequence of higher male mortality and longer female life spans with little effect of offspring sex ratio. Inconsistencies with previous studies are likely due to sampling methods and sampling design, which should be less of an issue with mark-recapture techniques. Together with other long-term mark-recapture studies, our study suggests that bias in offspring sex ratio rarely contributes to adult sex ratio in vertebrates. Rather, sex differences in adult survival rates and longevity determine vertebrate adult sex ratio. K E Y W O R D S :Life span, mark-recapture, population structure, sex-biased mortality, sex-biased recruitment, sex-ratio.

Sex ratio variation shapes the ecological effects of a globally introduced freshwater fish

“…This study adds to a growing literature suggesting that intraspecific variation may be important for shaping ecology [54][55][56]. Indeed, sexual dimorphism is one of the most common and well-known forms of intraspecific trait variation in the wild and many populations in nature show marked demographic differences in sex ratios from the commonly assumed expectation of 1 : 1 [2][3][4][5]7]. As such, we suggest that sex ratios may be a common driver of community and ecosystem variation across a wide diversity of organisms and habitat types.…”

The evolution of parental cooperation in birds

“…Unequal parental roles might lead to biased sex ratios because the sexes engage unequally in parental duties, have different time budgets, and consequently experience different mortality rates (50). Accordingly, sex-biased mortality rates are often correlated with biased ASR across populations and species (51)(52)(53). Moreover, some authors suggest positive feedbacks between changes in ASR and parental sex roles and thus the relationship may even be bidirectional (8,23,54).…”

Reproductive life history of Heterandria bimaculata (Heckel, 1848) (Poeciliinae: Poeciliidae) in the Honduran interior highlands: trait variation along an elevational gradient

“…This contrasts with the majority of studies on various poeciliids (Vargas & Sostoa 1996;Cabral & Marques, 1999;Zúñiga-Vega et al, 2012) and specifically for H. bimaculata (Gómez-Márquez et al, 1999), which report female-biased population structure. Female-biased sex ratios in poeciliids arise typically because males are more susceptible to mortality from numerous factors such as predation, resource limitation, hypoxia and extreme temperatures, largely because they devote such high energetic allocations to courtship Rodd & Reznick, 1997;Pettersson et al, 2004;Arendt et al, 2014). Alternatively, Arendt et al (2014) suggested that differential mortality rates between sexes can bias snapshot analyses of sex ratios, depending on sampling season.…”

“…Female-biased sex ratios in poeciliids arise typically because males are more susceptible to mortality from numerous factors such as predation, resource limitation, hypoxia and extreme temperatures, largely because they devote such high energetic allocations to courtship Rodd & Reznick, 1997;Pettersson et al, 2004;Arendt et al, 2014). Alternatively, Arendt et al (2014) suggested that differential mortality rates between sexes can bias snapshot analyses of sex ratios, depending on sampling season. Long-term analysis of the demographics of predator-free poeciliid populations would help to better describe the effects of predation on sex ratios.…”