Mate choice for body size leads to size assortative mating in the Ryukyu Scops Owl Otus elegans

Abstract

Understanding evolutionary phenomena that involve size assortative mating requires elucidating the generating mechanisms on which assortment is based. Although various mechanisms have been suggested, their relative importance may differ across taxonomic groups. Males selecting for large, fecund females combined with the dominance of large males in the competition for females has been suggested as a major mechanism in specific groups. However, raptors do not appear to conform to this, because the selection for smallness among males (assumed in a theory of reversed sexual size dimorphism) and the selection for largeness among males (assumed in the theory of size assortative mating) are in opposite directions. We studied the assortative mating during a long‐term study of the Ryukyu Scops Owls Otus elegans interpositus . Significant assortative mating was found for culmen length (from the base to the tip of the bill) and wing length (from the bend of the wing to the tip of the longest primary). Statistical control of the spatial and temporal accessibility of potential mates did not affect the assortment. Males with short wings had slightly higher fitness components than those with long wings, and females settling early tended to have small wings. Considering that early‐settling females can preferentially choose their mates, these results suggest that smaller females have an advantage when choosing smaller males with good reproductive performance. Improved flying and hunting ability of smaller individuals may be the background of choosing smaller individuals. We propose that, not passive process like similarity between individuals and their potential mates, but active mate choice for small individuals is an explanation for the assortative mating in this owl.

When is sympatric speciation a possible evolutionary outcome?

“…Matching rules apply when the choosy individuals in a population (females in this case) inspect their own phenotype, and accordingly pick a male to mate with [67]. Such matching rules have been used in models that describe speciation [42,68], and observed in ecology [69,70]. The mate choice of the female is determined only by its own trait value, and is not governed by another trait (like choosiness; however, the strength of assortative mating can vary [67].…”