Independent life history evolution between generations of bivoltine species: a case study of cyclical parthenogenesis

Abstract

Successive generations of bi- and multivoltine species encounter differing biotic and abiotic environments intra-annually. The question of whether selection can independently adjust the relationship between body size and components of reproductive effort within successive generations in response to generation-specific environmental variation is applicable to a diversity of taxa. Herein, we develop a conceptual framework that illustrates increasingly independent life history adjustments between successive generations of taxa exhibiting complex life cycles. We apply this framework to the reproductive biology of the gall-forming insect, Belonocnema treatae (Hymenoptera: Cynipidae). This bivoltine species expresses cyclical parthenogenesis in which alternating sexual and asexual generations develop in different seasons and different environments. We tested the hypotheses that ecological divergence between the alternate generations is accompanied by generational differences in body size, egg size, and egg number and by changes in the relationships between body size and these components of reproductive effort. Increased potential reproductive effort of sexual generation B. treatae is attained by increased body size and egg number (with no trade-off between egg number and egg size) and by a significant increase in the slope of the relationship between body size and potential fecundity. These generation-specific relationships, interpreted in the context of the model framework, suggest that within each generation selection has independently molded the relationships relating body size to potential fecundity and potential reproductive effort in B. treatae. The conceptual framework is broadly applicable to comparisons involving the alternating generations of bi- and multivoltine species.

Asymmetric, but opposing reductions in immigrant viability and fecundity promote reproductive isolation among host‐associated populations of an insect herbivore

“…Boxplot of predicted fecundity of resident and immigrant asexual generation females developing in each host plant environment. Fecundity was estimated as the total number of eggs contained by each individual female and was predicted using the relationship between body size and egg number developed in Hood and Ott (2017). P < 0.05 indicated by * for the comparison of residents and immigrants within the Qv host rearing environment.…”

“…To estimate potential fecundity of B. treatae as a function of the source population and rearing environment, we made use of the fact that asexual generation B. treatae are pro‐ovigenic (i.e., females emerge as adults with the entire potential lifetime complement of eggs fully matured), and that body size is highly correlated with egg number (an estimate of potential fecundity) (Hood and Ott 2017). Potential fecundity was estimated using the relationship: potential fecundity = −225.4 + 423.9 * tibia length (R 2 = 0.85, P < 0.0001) established by Hood and Ott (2017), where hind tibia length is used as an index of body size, a common method for Hymenoptera (Honek 1993). Here, estimating fecundity using body size is independent of our estimation of viability (proportional gall formation) as all individual wasps used to measure body size formed and successfully emerged from a gall.…”

Parallel host‐plant‐associated differences in an extended phenotype between populations of six species of gall‐forming insects

“…Gall size is one of the most important defensive phenotypes contributing to wasp survival (Stone et al, 2002; Stone & Schönrogge, 2003) and also likely to be positively correlated with body size, as was demonstrated in B. treatae and D. quercusvirens (Egan et al, 2013; Hood & Ott, 2010). Variation in gall size exhibited by one host‐associated population compared with the other could be due to differences in selection from natural enemy, selection for fecundity, or reduced fitness on non‐adapted hosts (Craig & Itami, 2011; Honěk, 1993; Hood & Ott, 2017; Marchosky & Craig, 2004) due to different host environments. However, bigger gall size was also found in multi‐chamber gall species such as A. quercuslanigera and C. quercusbatatoides , where the number of chambers rather than body size is more likely to be correlated with gall size (in A. quercuslanigera , the correlation between gall size and the number of chambers: r = 0.8288, p < 0.0001 [this study]; in C. quercusbatatoides , the correlation between gall size and the number of chambers: r = 0.69, p < 0.0001 [Weaver et al, 2020]).…”

Heterogony in Cycloneuroterus (Hymenoptera: Cynipidae: Cynipini) From Rearing Experiments and DNA Barcoding

“…gilvus have not yet been resolved. Interaction within these communities can influence the evolution of heterogonic life cycles in Cynipini (Forbes et al 2015, Hood and Ott 2017, Hood et al 2018). Because heterogony as an adaptation for avoidance of natural enemies is of broad interest, further study is needed to reveal the inquilines and parasitoids associated with sexual and asexual generations of heterogonic species of Cynipini as well as their life cycles.…”