Intra-Population Genetic Variation in the Temporal Pattern of Egg Maturation in a Parasitoid Wasp

Abstract

Parasitoid wasps are taxonomically and biologically extremely diverse. A conceptual framework has recently been developed for understanding life-history evolution and diversification in these animals, and it has confirmed that each of two linked life-history traits – the mode of larval development and the temporal pattern of egg maturation – acts as an organiser of life-history. The framework has been predicated on the assumption that there exists sufficient genetic variation in the latter trait to allow it to be shaped by natural selection. Focusing on the parasitoid wasp Trichogramma brassicae, our aim was to test the validity of that assumption, using established quantitative genetic methods. We demonstrate the existence of a statistically significant degree of intra-population polygenic variation in the temporal pattern of egg production within the wasp population we studied. Furthermore, our results, together with published data on clinal variation in the egg maturation pattern of another species, suggest that intra-specific evolutionary shifts in the temporal pattern of egg maturation of parasitoid wasps can result from a change in allocation to egg production either before, or very shortly after adult emergence, without there being an accompanying change in lifetime fecundity. As well as opening new avenues of research into the reproductive strategies, behaviour, community organisation and biological control potential of parasitoid wasps, this discovery also has implications for studies of life-history evolution and diversification in insects generally.

Size-induced phenotypic reaction norms in a parasitoid wasp: an examination of life-history and behavioural traits

“…Given that our strain T. podisi is almost completely synovigenic (Zhou et al ., ) and thus emerges with almost no mature eggs, we did not use egg load upon emergence (‘initial egg load’) as our measure of early‐life reproductive investment, as is standard for parasitoids that show moderate pro‐ovigeny (Jervis & Ferns, ; Jervis et al ., ). Rather, as a measure of ‘early‐life’ egg load, similar to the reproductive concentration index in Wajnberg, Curty & Jervis (), we counted the number of mature oocytes present after emergence but before any egg laying in hosts. We dissected 20 mated females that had emerged from each of the three host species’ eggs at two points along the trajectory of oocyte maturation: 3 days after emergence (before all oocytes had matured) and 9 days after emergence (when females were approaching their maximum egg load and almost all oocytes had matured).…”

Comparing parasitoid life histories

“…Although cross‐species variation in life histories is large, often so too is intraspecific variation (Harvey et al., ; Guinnee et al., ; Pexton & Mayhew, ; Thorne et al., ; Wajnberg et al., ). As the focus of comparative studies is understanding cross‐species variation, intraspecific variation tends to be ignored, and will contribute to the error term of analyses where species averages are less accurately estimated as a result.…”

The size‐number trade‐off and components of fitness in clonal parasitoid broods

“…We found C. bakeri to be weakly synovigenic, in which a modest proportion of the total eggs are produced after emergence (roughly 20%, comparing the day-1 total to the average of days 3 and 7; this corresponds to a 'reproductive concentration index' of about 0.8; Wajnberg et al, 2012). Though the congeneric C. floridanum is completely pro-ovigenic (Grbi c, 2003;Jervis et al, 2003), smaller koinobiont parasitoid species like C. bakeri are typically proovigenic (Jervis et al, , 2008.…”