Dawson, J. W. | bioRxiv Science

bioRxiv2023

Mimicry in motion: A grasshopper species that looks like, and moves like, a sympatric butterfly

Flash displays describe the sudden revealing of a conspicuous signal by an otherwise cryptic animal as it is fleeing from predators. One hypothesis for flash displays is that they have evolved to mislead predators into adopting an inappropriate search strategy following pursuit. Thus, if predators believe that the fleeing prey item will also be conspicuous when settled, then they will tend to give up searching sooner if they fail to find it. Naturally, if this hypothesis is correct then one might expect that the value of the flash display would cease once predators learn the flashers true resting appearance. However, even if predators are aware that the resting appearance of the signaller could be cryptic, flash displays will still be selected for if the flasher resembles another species that maintains its conspicuous appearance throughout. Motivated by this insight, we quantified the degree of chromatic and behavioral resemblance between the Carolina grasshopper (Dissosteira carolina) and mourning cloak butterfly (Nymphalis antiopa), a sympatric species with which it is commonly confused. The close similarity in both morphology and flight behavior (in the field and lab) between these distantly related species strongly suggests that they are in a mimetic relationship. It is unclear why this mimicry has evolved. One explanation is that mimicry has arisen through selection to maintain the efficacy of the flash display through search disruption even after predator learning. Another possibility is that the grasshopper has evolved to resemble the butterfly because the latter is harder to catch (evasive mimicry). However, we argue that pursuit and search disruption are entirely complementary explanations for the mimetic resemblance because they interfere with predation at two different stages of the attack sequence.

animal behavior and cognition↗

bioRxiv2020

A simple and dynamic thermal gradient device for measuring thermal performance in small ectotherms

The body temperature of ectothermic animals is heavily dependent on environmental temperature, impacting fitness. Laboratory exposure to favorable and unfavorable temperatures is used to understand these effects, as well as the physiological, biochemical, and molecular underpinnings of variation in thermal performance. Although small ectotherms, like insects, can often be easily reared in large numbers, it can be challenging and expensive to simultaneously create and manipulate several thermal environments in a laboratory setting. Here, we describe the creation and use of a thermal gradient device that can produce a wide range of constant or varying temperatures concurrently. This device is composed of a solid aluminum plate and copper piping, combined with a pair of programmable refrigerated circulators. As a simple proof-of-concept, we completed single experimental runs to produce a low-temperature survival curve for flies (Drosophila melanogaster) and explore the effects of daily thermal cycles of varying amplitude on growth rates of crickets (Gryllodes sigillatus). This approach avoids the use of multiple heating/cooling water or glycol baths or incubators for large-scale assessments of organismal thermal performance. It makes static or dynamic thermal experiments (e.g., creating a thermal performance or survival curves, quantifying responses to fluctuating thermal environments, or monitoring animal behaviour across a range of temperatures) easier, faster, and less costly.

ecology↗