Effects of rapid prey evolution on predator-prey cycles

We study the qualitative properties of population cycles in a predator-prey system where genetic variability allows contemporary rapid evolution of the prey. Previous numerical studies have found that prey evolution in response to changing predation risk can have major quantitative and qualitative effects on predator-prey cycles, including: (i) large increases in cycle period, (ii) changes in phase relations (so that predator and prey are cycling exactly out of phase, rather than the classical quarter-period phase lag), and (iii) "cryptic" cycles in which total prey density remains nearly constant while predator density and prey traits cycle. Here we focus on a chemostat model motivated by our experimental system [Fussmann et al. 2000,Yoshida et al. 2003] with algae (prey) and rotifers (predators), in which the prey exhibit rapid evolution in their level of defense against predation. We show that the effects of rapid prey evolution are robust and general, and furthermore that they occur in a specific but biologically relevant region of parameter space: when traits that greatly reduce predation risk are relatively cheap (in terms of reductions in other fitness components), when there is coexistence between the two prey types and the predator, and when the interaction between predators and undefended prey alone would produce cycles. Because defense has been shown to be inexpensive, even cost-free, in a number of systems [Andersson and Levin 1999, Gagneux et al. 2006,Yoshida et al. 2004], our discoveries may well be reproduced in other model systems, and in nature. Finally, some of our key results are extended to a general model in which functional forms for the predation rate and prey birth rate are not specified.Comment: 35 pages, 8 figure

Genetic, abiotic and social influences on sex differentiation in cichlid fishes and the evolution of sequential hermaphroditism

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73799/1/j.1467-2979.2005.00184.x.pd

Data from: Sustained costs of growth and the trajectory of recovery

1. Large body size is associated with many fitness advantages. Despite this, most species do not grow at their physiological maximum, suggesting costs to rapid growth. There are now many empirical examples of trade-offs with growth. 2. Despite the ubiquity of physiological delays, few studies have evaluated the duration over which growth costs occur. To address this question, we measured swimming ability in growth-manipulated Atlantic silversides (Menidia mendia). Fish were manipulated to grow at their maximum for two weeks and then were put on restricted rations so they grew slowly. We then compared swimming ability with fish that had always grown slowly. 3. Fast-grown fish had significantly poorer swimming ability, and continued to show a prolonged cost of this early period of rapid growth. We found that fish fully recovered normal swimming ability after ~1 month of growing slowly. Most surprisingly, the trajectory of recovery was not monotonic; performance actually decreased before it improved. 4. We conclude with a suggestion to develop a better understanding of the mechanisms linking growth to performance trade-offs. Our results suggest that reduced swimming performance following fast growth is unlikely to be completely explained by bioenergetic constraints. Additionally, there is need for more nuanced life history theory that incorporates prolonged growth costs to increase accuracy of growth rate prediction