Download (3398Kb) - ePrints Soton - University of Southampton
Download (3398Kb) - ePrints Soton - University of Southampton
Download (3398Kb) - ePrints Soton - University of Southampton
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Nearly all models <strong>of</strong> marine invertebrate reproductive patterns are characterized by<br />
having concave regions on the fitness curve, with the two major modes <strong>of</strong> planktonic<br />
larval development, planktotrophy and lecithotrophy always lying on opposite sides<br />
<strong>of</strong> the adaptive valley (McEdward and Miner, 2003). From this result, evolution<br />
between planktotrophy and lecithotrophy via natural selection would be predicted to<br />
be difficult or impossible, nevertheless phylogenetic analyses indicate that<br />
evolutionary transitions between these modes have occurred in a number <strong>of</strong> occasions<br />
(Wray, 1995; Rouse, 2000; McEdward and Miner, 2001).<br />
McEdward and Miner (2003) examined the effect <strong>of</strong> fluctuating food<br />
availability on the duration <strong>of</strong> the planktonic larval period and the number <strong>of</strong> <strong>of</strong>fspring<br />
that survive to metamorphosis in marine invertebrates with planktotrophic<br />
development, using fecundity-time models <strong>of</strong> reproductive strategies. The results<br />
showed that when food was abundant, smaller eggs were favoured and fluctuations in<br />
planktonic food concentrations affected small-egg strategies more strongly than largeegg<br />
strategies, though the variation in fitness was small in relation to fitness<br />
differences across egg sizes. Conversely, when food was strongly limited, larger eggs<br />
were favoured and fluctuations in planktonic food supply led to variations in fitness<br />
that were essentially related to fitness differences inherent in the strategies.<br />
McEdward and Miner (2003) concluded that when the extent <strong>of</strong><br />
environmentally-caused variations in reproductive success exceeds the differences in<br />
fitness among reproductive strategies, the adaptive landscape might be flattened, the<br />
intensity <strong>of</strong> disruptive or directional selection could be reduced and this should<br />
facilitate evolutionary transitions between planktotrophy and lecithotrophy or vice<br />
versa.<br />
77