1 May 2009 Group Selection on Population Size Affects Life-History Patterns in the Entomopathogenic Nematode Steinernema carpocapsae
Farrah Bashey, Curtis M. Lively
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Selection is recognized to operate on multiple levels. In disease organisms, selection among hosts is thought to provide an important counterbalance to selection for faster growth within hosts. We performed three experiments, each selecting for a divergence in group size in the entomopathogenic nematode, Steinernema carpocapsae. These nematodes infect and kill insect larvae, reproduce inside the host carcass, and emerge as infective juveniles. We imposed selection on group size by selecting among hosts for either high or low numbers of emerging nematodes. Our goal was to determine whether this trait could respond to selection at the group level, and if so, to examine what other traits would evolve as correlated responses. One of the three experiments showed a significant response to group selection. In that experiment, the high-selected treatment consistently produced more emerging nematodes per host than the low-selected treatment. In addition, nematodes were larger and they emerged later from hosts in the low-selected lines. Despite small effective population sizes, the effects of inbreeding were small in this experiment. Thus, selection among hosts can be effective, leading to both a direct evolutionary response at the population level, as well as to correlated responses in populational and individual traits.

© 2009 The Society for the Study of Evolution.
Farrah Bashey and Curtis M. Lively "Group Selection on Population Size Affects Life-History Patterns in the Entomopathogenic Nematode Steinernema carpocapsae," Evolution 63(5), 1301-1311, (1 May 2009). https://doi.org/10.1111/j.1558-5646.2009.00637.x
Received: 11 July 2008; Accepted: 1 January 2009; Published: 1 May 2009

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artificial selection
group selection
host-parasite interaction
levels of selection
population density
propagule size
Steinernema carpocapsae
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