Behavioral constraints on local adaptation and counter‐gradient variation: Implications for climate change

Abstract

Resource allocation to growth, reproduction, and body maintenance varies within species along latitudinal gradients. Two hypotheses explaining this variation are local adaptation and counter‐gradient variation. The local adaptation hypothesis proposes that populations are adapted to local environmental conditions and are therefore less adapted to environmental conditions at other locations. The counter‐gradient variation hypothesis proposes that one population out performs others across an environmental gradient because its source location has greater selective pressure than other locations. Our study had two goals. First, we tested the local adaptation and counter‐gradient variation hypotheses by measuring effects of environmental temperature on phenotypic expression of reproductive traits in the burying beetle, Nicrophorus orbicollis Say, from three populations along a latitudinal gradient in a common garden experimental design. Second, we compared patterns of variation to evaluate whether traits covary or whether local adaptation of traits precludes adaptive responses by others. Across a latitudinal range, N. orbicollis exhibits variation in initiating reproduction and brood sizes. Consistent with local adaptation: (a) beetles were less likely to initiate breeding at extreme temperatures, especially when that temperature represents their source range; (b) once beetles initiate reproduction, source populations produce relatively larger broods at temperatures consistent with their local environment. Consistent with counter‐gradient variation, lower latitude populations were more successful at producing offspring at lower temperatures. We found no evidence for adaptive variation in other adult or offspring performance traits. This suite of traits does not appear to coevolve along the latitudinal gradient. Rather, response to selection to breed within a narrow temperature range may preclude selection on other traits. Our study highlights that N. orbicollis uses temperature as an environmental cue to determine whether to initiate reproduction, providing insight into how behavior is modified to avoid costly reproductive attempts. Furthermore, our results suggest a temperature constraint that shapes reproductive behavior.

The thermal ecology of burying beetles: temperature influences reproduction and daily activity in Nicrophorus marginatus

“…However, at 26.5 ∘ C, we found that breeding pairs produced smaller broods when compared to the baseline treatment (26 ∘ C) but found no effect of temperature on individual offspring size. Brood size regulation in response to thermal cues has been documented for Nicrophorus orbicollis (Quinby et al, 2020). Consistent with our findings, this species was found to produce smaller broods at higher temperatures, however, individual offspring size (measured in mass) decreased at higher temperatures.…”

“…Reduced reproductive success at temperatures exceeding 27 ∘ C has been observed in other burying beetles species (Quinby et al, 2020) and could represent a byproduct of the physiological constraints imposed by thermal stress. However, when exposed to low and high thermal extremes, there is evidence that burying beetles are less likely to initiate reproduction in temperature extremes represented within their native environment (Quinby et al, 2020). The extremely low reproductive success rates documented for N. marginatus at 27.5 ∘ C could represent a behavioural strategy employed to avoid a costly reproductive event in an aversive environment.…”

“…In response to limited food availability, burying beetle parents have been documented to modulate brood size through infanticide (Creighton et al, 2009;Bartlett, 1987;Trumbo, 1990Trumbo, , 2006Robertson, 1993), and parental exposure to high levels of conspecific density resulted in smaller broods with individuals of increased body size (Woelber et al, 2018). Furthermore, there is evidence that burying beetles produce smaller broods and are less likely to initiate reproduction under thermal stress if they experience extreme temperatures in their local environment (Quinby et al, 2020). The results of these studies demonstrate that burying beetles modulate reproductive behaviours and offspring characteristics to be favourable in their perceived environments and do so based upon several interacting biotic and abiotic environmental factors.…”

The consequences of heatwaves for animal reproduction are timing‐dependent

“…Nicrophorus species showing that burying beetles are unlikely to initiate breeding in extreme environmental conditions (Quinby et al, 2020). Thus, the heatwave most likely delayed the onset of breeding, rather than lengthened the rate of offspring development.…”

Can recent evolutionary history promote resilience to environmental change?

“…Temperature was chosen as the environmental stressor because of its ecological relevance in the context of climate change. Insects, being poikilothermic, are particularly vulnerable to heat stress, and research on burying beetles specifically has shown that they have reduced breeding success at higher temperatures (Moss & Moore, 2021; Quinby et al, 2020; Sun & Kilner, 2020). We chose to expose the beetles to the temperature treatments during sexual maturation alone because this is the time when an adult beetle’s gonads are developing (e.g.…”