Pattern of inbreeding depression, condition dependence, and additive genetic variance in Trinidadian guppy ejaculate traits
Article first published online: 8 NOV 2013
© 2013 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Ecology and Evolution
Volume 3, Issue 15, pages 4940–4953, December 2013
How to Cite
Ecology and Evolution 2013; 3(15): 4940–4953
- Issue published online: 10 DEC 2013
- Article first published online: 8 NOV 2013
- Manuscript Accepted: 10 OCT 2013
- Manuscript Revised: 8 OCT 2013
- Manuscript Received: 27 JUN 2013
- University of Padova. Grant Numbers: CPDT058772, CPDR089052/08
- MIUR. Grant Number: PRIN 2008 - 2008Z8ACTN
- Fondazione CARIPARO. Grant Number: 217/08
- Genetic benefits;
- good sperm models;
- lek paradox;
- sperm competition
In polyandrous species, a male's reproductive success depends on his fertilization capability and traits enhancing competitive fertilization success will be under strong, directional selection. This leads to the prediction that these traits should show stronger condition dependence and larger genetic variance than other traits subject to weaker or stabilizing selection. While empirical evidence of condition dependence in postcopulatory traits is increasing, the comparison between sexually selected and ‘control’ traits is often based on untested assumption concerning the different strength of selection acting on these traits. Furthermore, information on selection in the past is essential, as both condition dependence and genetic variance of a trait are likely to be influenced by the pattern of selection acting historically on it. Using the guppy (Poecilia reticulata), a livebearing fish with high levels of multiple paternity, we performed three independent experiments on three ejaculate quality traits, sperm number, velocity, and size, which have been previously shown to be subject to strong, intermediate, and weak directional postcopulatory selection, respectively. First, we conducted an inbreeding experiment to determine the pattern of selection in the past. Second, we used a diet restriction experiment to estimate their level of condition dependence. Third, we used a half-sib/full-sib mating design to estimate the coefficients of additive genetic variance (CVA) underlying these traits. Additionally, using a simulated predator evasion test, we showed that both inbreeding and diet restriction significantly reduced condition. According to predictions, sperm number showed higher inbreeding depression, stronger condition dependence, and larger CVA than sperm velocity and sperm size. The lack of significant genetic correlation between sperm number and velocity suggests that the former may respond to selection independently one from other ejaculate quality traits. Finally, the association between sperm number and condition suggests that this trait may mediate the genetic benefits of polyandry which have been shown in this species.