Evidence for a male‐biased sex ratio in the offspring of a large herbivore: The role of environmental conditions in the sex ratio variation

Abstract

Numerous studies have examined whether the primary and/or secondary sex ratio in mammals, including humans, deviates from an equilibrium of 1:1. Although effect size in the sex ratio variation is expected to be low, a large sample size allows the identification of even small deviations from parity. In this study, we investigated whether the sex ratio of roe deer (Capreolus capreolus) offspring at birth approaches parity, using a large data set from roe deer offspring tagged in Baden‐Württemberg (Germany, 1972–2019, N = 12,437). In addition, a systematic re‐analysis of available data on the secondary sex ratios of roe deer was conducted to test whether our finding withstood the accumulation of further data. The null hypothesis that the sex ratio of roe deer (prenatal sex ratio and sex ratio at birth) approaches parity was rejected. Moreover, the secondary sex ratio of roe deer offspring deviated from the male‐biased mean for relatively cold or warm weather conditions during autumn and winter. Our study provides strong evidence for a male‐biased sex ratio in a large herbivore and weak evidence for variations in the secondary sex ratio owing to environmental conditions. The pattern is highly relevant in the context of climate change and its impact on the population dynamics of large herbivores.

Conservation Biology and Reproduction in a Time of Developmental Plasticity

“…Conversely, a significantly male-biased sex ratio of Asian elephants born in European zoos between 1962 and 2006 (ratio: 0.61, p = 0.044) was reported in 2009 [ 46 ], as well as an even more striking male bias in elephant births following artificial insemination (0.83, p = 0.003). It has clearly been very difficult for researchers to find a unifying theory that explains the differing reports of biased mammalian sex ratios at birth in diverse wild and captive species (see, for example [ 47 , 48 , 49 , 50 , 51 , 52 , 53 ]), in relation to environmental conditions. However, that such mechanisms exist and may sometimes, but not necessarily always, be adaptive, is now beyond dispute.…”

The Impact of Biologically Adaptive Sex Ratio Variation in Lamprey Population on Ecosystem Stability: Based on Lotka-Volterra Model

“…In recent years, adaptive sex ratio variation phenomenon is widely discovered and analyzed in many species. The research of Hagen R et al provides strong evidence for a male-biased sex ratio in a large herbivore and weak evidence for variations in the secondary sex ratio owing to environmental conditions [2]. The work by Wang YB et al, for the first time, conclusively demonstrates that two intracellular symbionts affect sex ratios in their whitefly hosts by regulating fertilization and supplying B vitamins.…”

Sex-specific DNA methylation and transcription of zbtb38 and effects of gene–environment interactions on its natural antisense transcript in zebrafish

“…In groups with TSD, extreme sex-ratio biases triggered by exposure to high temperatures are considered to be an important extinction driver [ 8 , 9 ]. Despite the fact that ESD is frequently presented as the result of an exposure that occurs at early developmental stages (i.e., during primordial germ cell development and gonad growth), exposure of parents (i.e., when the sex is already established and gonads are fully matured) can also affect the sex ratio of their offspring [ 10 , 11 ], also called sex ratio at birth [ 12 ]. Understanding the drivers and underlying mechanisms that trigger variations in offspring sex ratios is a long-standing challenge with important population implications [ 8 ].…”