Biology subjects

Powell, T. H.

Publications and source records attributed to Powell, T. H..

4 recordsLinked to original sources

bioRxiv2022

Simulated climate change causes asymmetric responses in insect life history timing potentially disrupting a classic ecological speciation system

Climate change may alter phenology within populations with cascading consequences for community interactions and on-going evolutionary processes. Here, we measured the response to climate change in two sympatric, recently diverged (~170 years) populations of Rhagoletis pomonella flies specialized on different host fruits (hawthorn and apple) and their parasitoid wasp communities. We tested whether warmer temperatures affect dormancy regulation and its consequences for synchrony across trophic levels and temporal isolation between divergent populations. Under warmer temperatures, both fly populations developed earlier. However, warming significantly increased the proportion of maladaptive pre-winter development in apple, but not hawthorn, flies. Parasitoid phenology was less affected, potentially generating ecological asynchrony. Observed shifts in fly phenology under warming may decrease temporal isolation, potentially limiting on-going divergence. Our findings of complex sensitivity of life-history timing to changing temperatures predict that coming decades may see multifaceted ecological and evolutionary changes in temporal specialist communities.

ecology↗

bioRxiv2022

Host-enemy interactions provide limited biotic resistance for a range-expanding species via reduced apparent competition

As species ranges shift in response to anthropogenic change, they lose coevolved or coadapted interactions and gain novel ones in recipient communities. Range-expanding species may lose or experience weak antagonistic interactions with competitors and enemies, and traits of interacting species will determine the strength of interactions. We leveraged a poleward range expansion of an oak gall wasp that co-occurs on its host plant with other gall wasp species and interacts with shared natural enemies (largely parasitoid wasps). We created quantitative host-parasitoid interaction networks by sampling galls on 400 trees. We compared network structure and function and traits of hosts and parasitoids in the native and expanded range. Interaction networks were less diverse in the expanded range, with low complementarity of parasitoid assemblages among hosts. While whole networks were more generalized in the expanded range, interactions with the range-expanding species were more specialized. This was not due to a loss of specialist enemies but weak apparent competition by shared generalist enemies. Phenological divergence of enemy assemblages attacking the novel and co-occurring hosts was greater in the expanded range that may contribute to weak apparent competition. Given the rate and extent of anthropogenic-driven range expansions, it is pressing to uncover how complex biotic interactions are reassembled.

ecology↗

bioRxiv2022

Latitudinal gradient in species diversity provides high niche opportunities for a range-expanding phytophagous insect

O_LIWhen species undergo poleward range expansions in response to anthropogenic change, they likely encounter less diverse communities in new locations. If low diversity communities provide weak biotic interactions, such as reduced competition for resources or predation, range-expanding species may experience high niche opportunities. C_LIO_LIHere, we uncover if oak gall wasp communities experience a latitudinal diversity gradient (LDG) and weaker interactions at the poles that might create high niche opportunities for a range-expanding community member. C_LIO_LIWe performed systematic surveys of oak gall wasps on a dominant oak, Quercus garryana, throughout most of its range, from northern California to Vancouver Island, British Columbia. On 540 trees at 18 sites, we identified 23 species in three guilds (leaf detachable, leaf integral, and stem galls). We performed regressions between oak gall wasp diversity, latitude, and other abiotic and habitat factors to reveal if cynipid communities follow an LDG. To uncover patterns in local interactions, we performed partial correlations on oak gall wasps co-occurring on trees within regions. Finally, we performed regressions between abundances of co-occurring gall wasps on trees to reveal potential interactions. C_LIO_LIQ. garryana-gall wasp communities followed an LDG, with lower diversity at higher latitudes, particularly with a loss of detachable leaf gall species. Detachable leaf gall wasps, including the range-expanding species, co-occurred most on trees and had weak interactions in the northern region. Abundances of the range-expander and detachable and integral leaf galls co-occurring on trees were negatively related, suggesting antagonistic interactions. Overall, we found that LDGs create communities with weaker antagonistic interactions at the poles that might facilitate ecological release in a range-expanding community member. C_LIO_LIHere, we uncover how regional and local scale patterns and processes create high niche opportunities for a range-expanding community member. This research provides insight into how biogeographical patterns in communities and species interactions influence the outcome of range expansions. Given the ubiquity of LDGs, these outcomes might be expected in other phytophagous insect communities. C_LI

ecology↗

bioRxiv2020

A rapidly evolved shift in life history timing during ecological speciation is driven by the transition between developmental phases

For insect species in temperate environments, seasonal timing is often governed by the regulation of diapause, a complex developmental program that allows insects to weather unfavorable conditions and synchronize their lifecycles with available resources. Diapause consists of a series of phases that govern initiation, maintenance, and termination of this developmental pathway. The evolution of insect seasonal timing depends in part on how these phases of diapause development and post-diapause development interact to affect variation in phenology. Here, we dissect the physiological basis of a recently evolved phenological shift in Rhagoletis pomonella (Diptera: Tephritidae), a model system for ecological divergence. A recently derived population of R. pomonella shifted from specializing on native hawthorn fruit to earlier fruiting introduced apples, resulting in a 3-4 week shift in adult emergence timing. We tracked metabolic rates of individual flies across post-winter development to test which phases of development may act either independently or in combination to contribute to this recently evolved divergence in timing. Apple and hawthorn flies differed in a number of facets of their post-winter developmental trajectories. However, divergent adaptation in adult emergence phenology in these flies was due almost entirely to the end of the pupal diapause maintenance phase, with post-diapause development having a very small effect. The relatively simple underpinnings of variation in adult emergence phenology suggest that further adaptation to seasonal change in these flies for this trait might be largely due to the timing of diapause termination unhindered by strong covariance among different components of post-diapause development. Data accessibilityAll data (in the form of tables of all metabolic rate measurements for all individual flies in the study) will be available on DRYAD when the manuscript is published.

evolutionary biology↗