Big mums give their young a better start in life

Posted on September 21, 2011

In principle, if the age or size of reproducing animals affects their ability to produce viable offspring, then the dynamics of a population will depend on its age or size structure.  Although this proposition has received theoretical support, so far it hasn’t been endorsed by  much real-world evidence.  Canadian researchers used walleye (Sander vitreus, a perch-like fish), to look for evidence of maternal influences on offspring survival.  Walleye eggs were fertilised and incubated in the lab, and after four days the larvae were stocked in 0.5 ha ponds.  Sixty- two days later, juvenile fish were collected from the ponds and assigned to known parents using microsatellite DNA analysis.  The data showed that the probability of juvenile survival over the two-month period was strongly related to the size of the original egg and, to a lesser extent, the egg’s fat content.  Together with other evidence that large walleye tend to produce large, fatty eggs, these findings lent support to the maternal influence hypothesis.  To see if the maternal influence on larval survival was strong enough to have a significant effect on population dynamics, the data were used to build a population model that allowed the researchers to examine the predicted effects of selective harvesting on the stock-recruitment relationship of walleye.  This revealed that when older age classes were protected from harvest the maximum reproductive rate of the population (i.e., the maximum number of recruits relative to the number of eggs) was 1.2 times higher than when the older fish were harvested.  When used to simulate the impact on a real exploited population (walleye in Lake Erie) the model predicted that the maximum reproductive rate could be increased by a factor of 2.8 by raising the mean age of adult females from 3.0 to 4.4 years.  It therefore seems that the age or size of females can be an important driver of population dynamics, which means that exploited stocks could benefit from management strategies that protect, rather than target, reproductively valuable individuals.

 Reference:  Venturelli, P.A., Murphy, C.A., Shuter, B.J., Johnston, T.A., Van Coeverden De Groot, P.J., Boag, P.T., Casselman, J. M., Montgomerie, R., Wiegand, M.D. & Leggett, W.C.  2010.  Maternal influences on population dynamics: evidence from an exploited freshwater fish.  Ecology, 91(7), 2003–2012.