Exploring context dependency in eco‐evolutionary patterns with the stick insect Timema cristinae

Rapid evolution can influence the ecology of populations, communities, and ecosystems, but the importance of evolution for ecological dynamics remains unclear, largely because the contexts in which evolution is powerful are poorly resolved. Here, we carry out a large observational study to test hypotheses about context dependency of eco‐evolutionary patterns previously identified on the stick insect Timema cristinae . Experiments and observations conducted in 2011 and 2012 documented predator‐mediated negative effects of camouflage maladaptation (i.e., evolutionary dynamics) on: (a) T. cristinae abundance and, (b) species richness and abundance of other arthropods. Here we show that camouflage maladaptation does not correlate with T. cristinae abundance and, instead, is associated with increased abundance and species richness of cohabitating arthropods. We furthermore find that plants with high levels of Timema maladaptation tend to have higher foliar nitrogen, that is, higher nutritional value, and more positive mass‐abundance slopes in the coexisting arthropod communities. We propose explanations for the observed contrasting results, such as negative density‐ and frequency‐dependent selection, feedbacks between herbivore abundance and plant nutritional quality, and common effects of predation pressure on selection and prey abundance. Our results demonstrate the utility of observational studies to assess the context dependency of eco‐evolutionary dynamics patterns and provide testable hypotheses for future work

Riparian reserves protect butterfly communities in selectively logged tropical forest

1. Selective logging is the most widespread habitat disturbance in tropical forests. Primary forest set-asides along riparian zones are mandated in many countries and a key question is whether these riparian reserves provide biodiversity conservation benefits. 2. We characterise butterfly communities in fixed-width riparian reserves of 30 m on each bank along narrow streams (<10 m) paired with interior logged forest transects, and in primary forests within a selective logging concession in the south-western Brazilian Amazon. 3. We found that primary forest species richness was more similar to riparian reserves than to paired interior logged forest points, whereas abundance remained higher in both riparian reserves and interior logged points, likely due to the intrusion of canopy-dwelling species in disturbed habitats, as previously reported in the literature. Butterfly assemblages within riparian reserves were more similar to unlogged primary forests than interior logged points, and canopy height in riparian reserves was associated with increased assemblage similarity to primary forest points. 4. Changes in abundance relative to primary forest were of a larger magnitude in interior logged points than in riparian reserves within logged forests, highlighting the role of riparian reserves in maintaining primary forest-like communities. We found no particular primary forest butterfly clades to be more sensitive to changes in abundance than other clades. 5. Synthesis and applications. Mandatory conservation set-asides around streams or rivers (riparian buffers) have an important role in protecting the abundance and composition of primary forest butterfly assemblages within selective logging concessions in tropical rainforests. This study highlights the need to assess the conservation value of protecting unlogged riparian forest strips in other taxa to inform policy

Heat stress reduced survival but sped up development in Heliconius erato butterflies

Publication status: PublishedFunder: Balfour‐Browne summer grant from the Zoology Department, University of CambridgeAbstractAnthropogenic climate change is thought to present a significant threat to biodiversity, in particular to tropical ectotherms, and the effects of long‐term developmental heat stress on this group have received relatively little research attention. Here, we studied the effects of experimentally raising developmental temperatures on a tropical butterfly. We measured survival, development time, adult body mass and wing size of Heliconius erato demophoon (Linnaeus) (Lepidoptera: Nymphalidae) across three temperature treatments. Egg survival was lower in the hotter treatments, with 84%, 73% and 49% of eggs hatching in the 20–30°C (fluctuating temperature with 12 h at 20°C followed by 12 h at 30°C), 23–33°C and 26–36°C treatments, respectively. Larval survival was three times lower in the 26–36°C treatment (8%) compared with the 20–30°C treatment (26%), and we did not detect differences in pupal survival across treatments due to high mortality in earlier stages. Under a moderately increased temperature at 23–33°C, larvae developed faster and adults had a higher body mass and wing loading, but this was not seen in the hottest treatment (26–36°C). Females were also heavier than males in the 23–33°C treatment, but there was no associated increase in wing size. This may suggest a different developmental response to moderately elevated temperatures between the sexes. In summary, high developmental temperatures are particularly lethal for eggs and less so for larvae and also affect adult morphology. This highlights the importance of understanding the effects of temperature variation across ontogeny in tropical ectotherms.</jats:p

Genomics of altitude-associated wing shape in two tropical butterflies

Understanding how organisms adapt to their local environment is central to evolution. With new whole-genome sequencing technologies and the explosion of data, deciphering the genomic basis of complex traits that are ecologically relevant is becoming increasingly feasible. Here, we studied the genomic basis of wing shape in two Neotropical butterflies that inhabit large geographical ranges. Heliconius butterflies at high elevations have been shown to generally have rounder wings than those in the lowlands. We reared over 1,100 butterflies from 71 broods of H. erato and H. melpomene in common-garden conditions and showed that wing aspect ratio, that is, elongatedness, is highly heritable in both species and that elevation-associated wing aspect ratio differences are maintained. Genome-wide associations with a published data set of 666 whole genomes from across a hybrid zone, uncovered a highly polygenic basis to wing aspect ratio variation in the wild. We identified several genes that have roles in wing morphogenesis or wing aspect ratio variation in Drosophila flies, making them promising candidates for future studies. There was little evidence for molecular parallelism in the two species, with only one shared candidate gene, nor for a role of the four known colour pattern loci, except for optix in H. erato. Thus, we present the first insights into the heritability and genomic basis of within-species wing aspect ratio in two Heliconius species, adding to a growing body of evidence that polygenic adaptation may underlie many ecologically relevant traits

Impacts of selective logging management on butterflies in the Amazon

Selective logging for timber production affects vast areas across the tropics, yet we lack detailed understanding of the impacts of logging intensity on biodiversity. These impacts can be studied at two levels: the impacts of logging intensity on overall diversity and community composition; and how logging intensity affects individual species' abundance-logging yield relationships. The latter underpins whether land-sharing logging (i.e. low intensity throughout) or land-sparing logging (i.e. high intensity with retention of some primary forest) is the optimal strategy. We examine both levels to determine the impacts of local-scale logging intensity on butterflies in Rondônia, Brazil, the global epicenter of butterfly alpha-diversity. Overall butterfly abundance was highest at intermediate logging intensity, whereas species richness increased after logging but was not affected by logging intensity, and that species composition increasingly changed from the primary community composition at higher logging intensities. Using individual species' abundance-yield curves, we then simulated species responses to a suite of logging strategies, ranging from total sharing to total sparing. Logging simulations predicted that more butterfly species would benefit from low-intensity land-sharing logging, having higher abundances than under land-sharing scenarios. However, some butterfly clades benefited disproportionally from the retention of primary forest within land-sparing logging concessions. Butterflies overall may benefit from intermediate logging strategies that promote a combination of low and high intensity logged areas, with some protected primary forest

Repeated genetic adaptation to high altitude in two tropical butterflies

Repeated evolution can provide insight into the mechanisms that facilitate adaptation to novel or changing environments. Here we study adaptation to altitude in two tropical butterflies, Heliconius erato and H. melpomene, which have repeatedly and independently adapted to montane habitats on either side of the Andes. We sequenced 518 whole genomes from altitudinal transects and found many regions differentiated between highland (~ 1200 m) and lowland (~ 200 m) populations. We show repeated genetic differentiation across replicate populations within species, including allopatric comparisons. In contrast, there is little molecular parallelism between the two species. By sampling five close relatives, we find that a large proportion of divergent regions identified within species have arisen from standing variation and putative adaptive introgression from high-altitude specialist species. Taken together our study supports a role for both standing genetic variation and gene flow from independently adapted species in promoting parallel local adaptation to the environment

Repeated genetic adaptation to high altitude in two tropical butterflies.

Repeated evolution can provide insight into the mechanisms that facilitate adaptation to novel or changing environments. Here we study adaptation to altitude in two tropical butterflies, Heliconius erato and H. melpomene, which have repeatedly and independently adapted to montane habitats on either side of the Andes. We sequenced 518 whole genomes from altitudinal transects and found many regions differentiated between highland (~ 1200 m) and lowland (~ 200 m) populations. We show repeated genetic differentiation across replicate populations within species, including allopatric comparisons. In contrast, there is little molecular parallelism between the two species. By sampling five close relatives, we find that a large proportion of divergent regions identified within species have arisen from standing variation and putative adaptive introgression from high-altitude specialist species. Taken together our study supports a role for both standing genetic variation and gene flow from independently adapted species in promoting parallel local adaptation to the environment