Fluid Dynamics and the Potential Cost of Long Genitalia in Male Guppies

Male guppies with long genitals may swagger, physically in a current, and metaphorically in the grand scheme of reproduction. Or not. This newly published study explores these questions:

A Potential Cost of Long Genitalia in Male Guppies: the Effects of Current Speed on Reproductive Behaviour,” Lucia Kwan, Adam N. Dobkin, F. Helen Rodd, and Locke Rowe, Ethology, epub October 13, 2016. The authors explain:


“genital elongation may come at a cost of reduced locomotor abilities (e.g. resulting from greater drag and resistance). In this study, we were interested in the potential role of natural selection on the evolution of gonopodium length in poeciliids. Specifically, we asked whether a greater genital length impedes male reproductive behaviours at higher flow rates in the Trinidadian guppy, Poecilia reticulata. Using a flow chamber, males were placed with females in low- and high-flow regimes and reproductive behaviours were measured. We did not find evidence for a cost of bearing a longer gonopodium at high flow. However, males did alter their mating tactics in response to current flow.”

(Thanks to Sara Lewis for bringing this to our attention.)