Abstract
Proportions between pairs of digits are linked to fitness in tetrapods and they can be influenced by sex hormones through individuals’ ontogenies. Therefore, in many species, the proportions amongst finger length ratios (referred as digit ratio, i.e. 2D second and 4D fourth digits) can differ between males and females. We investigated whether the three most commonly used forelimb digit ratios are sexually dimorphic in three tropidurid species. In one of the three lizard species, Eurolophosaurus nanuzae, males and females differ for only 2D:4D digit ratio. Otherwise, our results on the studied Tropidurus species conform to previous studies showing no differences in digit ratios between males and females. Hence, it might be the case of local selective forces shaping interpopulation variation in the expression of sexual dimorphism for digit ratio.
Highlights
IntroductionThe ratio between the lengths of pairs of fingers (referred to as digit ratio, i.e. 2D second and 4D fourth digits) depends on differential effects of variations in concentrations of prenatal steroids during embryonic stages (Manning et al 1998, 2003, Manning 2002)
Sexual dimorphism for the proportion between digit length was found for Podarcis siculus (Rafinesque-Schmaltz, 1810) and Podarcis melisellensis (Braun, 1877), with males presenting a higher digit ratio than females (Van Damme et al 2015)
Males of T. torquatus had larger body sizes than females, but we found no intersexual dimorphism for any digit ratio (Table 1)
Summary
The ratio between the lengths of pairs of fingers (referred to as digit ratio, i.e. 2D second and 4D fourth digits) depends on differential effects of variations in concentrations of prenatal steroids during embryonic stages (Manning et al 1998, 2003, Manning 2002). Burley and Foster (2004) showed for the bird species Taeniopygia guttata castanotis (Gould, 1837) that the ratio between digits of females is associated with their preferences for a given male phenotype. For this species, the digit ratio correlates with song rate, a secondary sexual trait of the species (Forstmeier 2005). Digit ratios of females were larger than those of males, for example, Anolis humilis Peters, 1863 – Direnzo and Stinosky (2012) – and Trachylepis planifron (Parker, 1942) – Rubolini et al (2006). Sexual dimorphism for digit ratio evolved in association with ecological divergence amongst iguanian lizards and it might be attributable to the differential
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