Dispersal is not female biased in a resource-defence mating ungulate, the European roe deer

Abstract

Dispersal is frequently more prevalent in one sex compared to the other. Greenwood proposed that patterns of sex-biased dispersal among birds and mammals are linked to their mating strategies. For species where males defend resources rather than females, he predicted female-biased dispersal, because males should remain at their birth site where they are familiar with the distribution of the resources that they must defend. Greenwood's hypothesis has been extensively supported among birds, where most species exhibit a resource-defence mating strategy. However, almost no equivalent information is available for mammals as males generally defend mates in this group. An exception is the European roe deer, a resource-defence mating ungulate. We thus tested Greenwood's hypothesis on this atypical mammalian model, looking for female-biased dispersal using sex-specific inter-individual genetic distances. We conclusively show that gene flow is not higher among females compared to males in the studied roe deer population, and hence that dispersal is not female-biased, suggesting that male mating strategy is not the primary selective force driving the evolution of dispersal in roe deer. We discuss the role of female mate choice and intra-sexual competition as possible alternative selective pressures involved.

Figure 1

Geographical location of the study site and sampling of roe deer individuals in south-western France. Woodland habitat is represented by grey shading, male samples by full squares and female samples by open squares (at least one roe deer was genotyped at each location). Scale bar, 3 km.

Figure 2

Distribution of d_i for each test. d_i values are expected to be significantly greater than zero under the female-biased dispersal hypothesis. For each graph, the number of d_i values greater and lower than zero are indicated (N). (a) Genetic differentiation a_r at the local scale, $d_i={\overline{a}}_{\text{r}}{(f)}_i-{\overline{a}}_{\text{r}}{(m)}_i$; (b) genetic relatedness r_w at the local scale, $d_i={\overline{r}}_{\text{w}}{(m)}_i-{\overline{r}}_{\text{w}}{(f)}_i$; (c) genetic differentiation a_r at the regional scale, $d_i={\overline{a}}_{\text{r}}{(m)}_i-{\overline{a}}_{\text{r}}{(f)}_i$; (d) genetic relatedness r_w at the regional scale, $d_i={\overline{r}}_{\text{w}}{(f)}_i-{\overline{r}}_{\text{w}}{(m)}_i$; (e) geographic distances, $d_i=\overline{g}{(m)}_i-\overline{g}{(f)}_i$; (f) absolute residuals of the regression genetic distance/ln(geographic distance), $d_i=\overline{s}{(m)}_i-\overline{s}{(f)}_i$; (g) geographic distances of related individuals, $d_i=\overline{g}\text{rel}{(f)}_i-\overline{g}\text{rel}{(m)}_i$. ${\overline{a}}_{\text{r}}{(m)}_i$ and ${\overline{a}}_{\text{r}}{(f)}_i$ are the mean genetic differentiations a_r for males and females, respectively, for the ith resampling set; ${\overline{r}}_{\text{w}}{(m)}_i$ and ${\overline{r}}_{\text{w}}{(f)}_i$ are the mean genetic relatedness r_w for males and females respectively, for the ith resampling set; $\overline{g}{(m)}_i$ and $\overline{g}{(f)}_i$ are the mean geographic distances for males and females respectively, for the ith resampling set; $\overline{s}{(m)}_i$ and $\overline{s}{(f)}_i$ are the mean absolute values of the residuals from the regression of genetic differentiation on ln(geographic distance) for males and females respectively, for the ith resampling set; $\overline{g}\text{rel}{(m)}_i$ and $\overline{g}\text{rel}{(f)}_i$ are the mean geographic distances of related individuals for males and females, respectively.

Figure 3

Conceptual model to describe density-dependent sex-specific dispersal in roe deer, after Wahlström & Liberg (1995): male (crosses) and female (circles) dispersal for three levels of density. At low densities, dispersal should be male-biased, while at intermediate to high densities there should be no sex difference (see text for a detailed explanation).