Escaping the evolutionary trap: Can size-related contest advantage compensate for juvenile mortality disadvantage when parasitoids develop in unnatural invasive hosts?

The quality of hosts for a parasitoid wasp may be influenced by attributes such as host size or species, with high quality for successful development usually coincident with high quality for larger offspring. This is not always the case: for the Scelionid wasp Trissolcus basalis, oviposition in eggs of the Brown Marmorated Stink Bug, Halyomorpha halys, rather than of the normal host, the Southern Green Stink Bug, Nezara viridula, leads to lower offspring survival, but survivors can be unusually large. Adult female T. basalis engage in contests for host access. As larger contestants are typically favoured in contests between parasitoids, the larger size of surviving offspring may compensate for the mortality of others. We construct a general game-theoretic model to explore whether size advantage can sustain a maternal preference to utilize a more deadly host species. We find that size advantage alone is unlikely to sustain a shift in host preference, yet such an outcome is possible when size asymmetries act simultaneously with advantages in host possession (ownership effect). Halyomorpha halys is an invasive pest of major agro-economic importance in Europe and the Americas, and use of its eggs as hosts by native parasitoids such as T. basalis has been seen as an evolutionary trap due to their high developmental mortality. Our model suggests that the recently discovered effect of host choice on offspring size may provide an escape from the trap via effects on contest biology of T. basalis which could foster a more stable association with H. halys. An evolutionary shift in the reproductive value of H. halys could increase the efficiency of T. basalis as a biological control agent of this invasive stink bug pest

The ecogenetic link between demography and evolution : can we bridge the gap between theory and data?

Calls to understand the links between ecology and evolution have been common for decades. Population dynamics, i.e. the demographic changes in populations, arise from life history decisions of individuals and thus are a product of selection, and selection, on the contrary, can be modified by such dynamical properties of the population as density and stability. It follows that generating predictions and testing them correctly requires considering this ecogenetic feedback loop whenever traits have demographic consequences, mediated via density dependence (or frequency dependence). This is not an easy challenge, and arguably theory has advanced at a greater pace than empirical research. However, theory would benefit from more interaction between related fields, as is evident in the many near-synonymous names that the ecogenetic loop has attracted. We also list encouraging examples where empiricists have shown feasible ways of addressing the question, ranging from advanced data analysis to experiments and comparative analyses of phylogenetic data

Kinship effects in quasi-social parasitoids II : co-foundress relatedness and host dangerousness interactively affect host exploitation

Sclerodermus brevicornis is a parasitoid that exhibits cooperative multi-foundress brood production. Prior work showed that the time lag to paralysis of small-sized hosts is shorter when co-foundress relatedness is higher and predicted that the greater risks and greater benefits of attacking larger hosts would combine with co-foundress relatedness to determine the limits to the size of a host that a female is selected to attack as a public good. It was also predicted that the time to host attack would be affected by an interaction between host size and relatedness. Here, we show empirically that both host size and kinship affect S. brevicornis reproduction and that they interact to influence the timing of host attack. We also find effects of co-foundress relatedness after hosts have been suppressed successfully. A public goods model using parameters estimated for S. brevicornis again suggests that selection for individual foundresses to attack and, if successful, to share hosts will be dependent on both the size of the host and the relatedness of the foundresses to any co-foundresses present. Females will not be selected to bear the individual cost of a public good when hosts are large and dangerous or when their relatedness to the co-foundress is low. We conclude that although reproductive behaviours exhibited by Sclerodermus females can be cooperative, they are unlikely to be exhibited without reference to kinship or to the risks involved in attempting to suppress and share large and dangerous hosts

Testing predictions of small brood models using parasitoid wasps

Question: How is variation in offspring size (between broods) related to brood size? Hypotheses: Variance in offspring size (between broods) should decrease with increasing brood size as predicted by Charnov and colleagues' (Charnov and Downhower, 1995; Charnov et al., 1995) small brood invariant. The range in resources put towards reproduction (for mothers producing a certain brood size) should be invariant over brood size (Downhower and Charnov, 1998). We also test assumptions underlying these predictions. Data studied: We use previously collected data on six parasitoid wasp species. Conclusions: As predicted, variance in offspring size among broods decreased with increasing brood size. However, this decrease did not follow closely the quantitative predictions of Charnov and colleagues (Charnov and Downhower, 1995; Charnov et al., 1995). We found some support for the prediction that the range in resources invested in reproduction is invariant over brood size. The assumption that mean offspring size is constant over brood size was violated in three of six species. The assumpt [KEYWORDS: brood size ; litter size ; parasitoid wasps ; resource allocation ; trade-off OPTIMAL OFFSPRING SIZE ; CLUTCH-SIZE ; SEX-CHANGE ; BODY-SIZE ; HYMENOPTERA ; EVOLUTION ; FITNESS ; FIELD ; INVARIANTS ; EULOPHIDAE

Testing predictions of small brood models using parasitoid wasps

Question: How is variation in offspring size (between broods) related to brood size? Hypotheses: Variance in offspring size (between broods) should decrease with increasing brood size as predicted by Charnov and colleagues' (Charnov and Downhower, 1995; Charnov et al., 1995) small brood invariant. The range in resources put towards reproduction (for mothers producing a certain brood size) should be invariant over brood size (Downhower and Charnov, 1998). We also test assumptions underlying these predictions. Data studied: We use previously collected data on six parasitoid wasp species. Conclusions: As predicted, variance in offspring size among broods decreased with increasing brood size. However, this decrease did not follow closely the quantitative predictions of Charnov and colleagues (Charnov and Downhower, 1995; Charnov et al., 1995). We found some support for the prediction that the range in resources invested in reproduction is invariant over brood size. The assumption that mean offspring size is constant over brood size was violated in three of six species. The assumpt [KEYWORDS: brood size ; litter size ; parasitoid wasps ; resource allocation ; trade-off OPTIMAL OFFSPRING SIZE ; CLUTCH-SIZE ; SEX-CHANGE ; BODY-SIZE ; HYMENOPTERA ; EVOLUTION ; FITNESS ; FIELD ; INVARIANTS ; EULOPHIDAE]