Parthenogenetic Darevskia lizards mate frequently if they have the chance: a quantitative analysis of copulation marks in a sympatric zone

Abstract

Several Caucasian rock lizards of the genus Darevskia of hybrid origin are known to reproduce parthenogenetically. Local communities can be composed exclusively of parthenogens, though syntopy with bisexual members of the genus may occur. In some localities, reproduction between bisexual and parthenogenetic Darevskia has been previously reported based on lizard intermediate morphology and karyology (3n, 4n). However, the frequency of such heterospecific matings remains unknown. We indirectly quantified the reproductive interactions through the inspection of copulation marks in females in a mixed Darevskia community from Kuchak (Armenia) composed of two hybrid parthenogens (D. armeniaca and D. unisexualis), one bisexual species (D. valentini) and their putative backcrosses. A total of 139 adults were randomly collected and photographed. Females were later measured (SVL), inspected for inguinal marks and ranked from 0 (no scars) to 3 (≥ 3 scars). The lizard species and ploidy determination was ensured by a parallel microsatellite analysis. Sex-ratio in the community was extremely biased due to the high abundance of parthenogenetic females. All female types displayed copulation marks with frequencies varying from 80% in D. valentini to 64% in D. armeniaca. Remarkably, 7 out of 11 (64%) backcross females also showed marks. In the most abundant D. armeniaca, the prevalence and intensity of copulation marks increased with body size, just as predicted for polygynous female lacertids. These results indicate that copulation between parthenogenetic and bisexual species in Darevskia mixed communities is common and driven by sexual selection, thus reinforcing previous suggestions of reproductive interaction in syntopy. Evolutionary implications of these findings are discussed.