Correlations between sex rate estimates and fitness across predominantly parthenogenetic flatworm populations

Abstract

One explanation for the success of sexual reproduction is that sex increases the efficacy of natural selection. Recombination and segregation lead to fitness variance among offspring which then offers a wider target for natural selection. Consequently, adaptation to changing environments is accelerated and population mean fitness will increase. We investigated whether low levels of sex are associated with increased fitness variance and mean in parthenogenetic biotypes of the planarian flatworm Schmidtea polychroa. Parthenogenetic S. polychroa are triploid and reproduce clonally with occasional sexual reproduction. By‐products and measures of occasional sex are the local presence of tetraploids and elevated levels of genotypic diversity. We correlated the proportion of tetraploids and genotypic diversity with fitness attributes of six genetically differentiated locations within one meta‐population. Results indicate strong, positive correlations with variance and with mean offspring number produced during a 5‐week period. The ecological and evolutionary implications for the maintenance of parthenogenetic S. polychroa are discussed.

Unraveling the mysteries of reproduction

“…This might actually mean that a very small degree of sexual reproduction (or recombination) has tremendous effects. Similar results have been obtained in theoretical (Bengtsson, 2003) as well as empirical studies (D'Souza and Michiels, 2008). The degree of sexuality required to transform entire systems is certainly a topic worth pursuing further.…”

Genetic and phenotypic influences on clone‐level success and host specialization in a generalist parasite

“…, 2010). However, heterozygosity–fitness correlations are also relevant to ecological and evolutionary issues in noninbred populations (see D’Souza & Michiels, 2008). An earlier mesocosm study of host preference, in which M. novaezealandensis cercariae were simultaneously exposed to both P. novizealandiae and H. stephenseni, showed no correlation with heterozygosity (Koehler et al.…”

“…Previous studies investigating the relationship between genetic diversity (heterozygosity) and fitness traits typically involve populations that are inbred or recently bottlenecked, as heterozygosity is often used as an indicator of inbreeding depression (Hansson & Westerberg, 2002;Chapman et al, 2009;Szulkin et al, 2010). However, heterozygosity-fitness correlations are also relevant to ecological and evolutionary issues in noninbred populations (see D'Souza & Michiels, 2008). An earlier mesocosm study of host preference, in which M. novaezealandensis cercariae were simultaneously exposed to both P. novizealandiae and H. stephenseni, showed no correlation with heterozygosity (Koehler et al, 2011a).…”

Differential expression of heat shock protein 70 in relation to stress type in the flatworm Schmidtea polychroa

“…Only parthenogenetic biotypes exist at this site (Beukeboom et al, 1996;. The location is characterized by high genotypic diversity (Pongratz et al, 2003;D'Souza & Michiels, 2008), caused by occasional sexual exchange between parthenogens (D'Souza et al, 2004;. Flatworms were collected from the underside of stones using brushes.…”