Two recent studies analyze character shifts in response to different selection regimes – (1) Mullerian mimicry wing patterns in Heliconius butterflies, and (2) anti-intraguild-predator adaptations in armor and shape of threespine sticklebacks.
Mullerian mimicry in Heliconius butterflies. Image courtesy: Wikipedia (https://upload.wikimedia.org/wikipedia/commons/0/0a/Heliconius_mimicry.png)
Hoyal Cuthill and Charleston 2015 Wing patterning genes and coevolution of Mullerian mimicry in Heliconius butterflies: support from phylogeography, co-phylogeny and divergence times
The Heliconius butterfly radiation across the neotropics has been characterized extensively, especially in their fascinating diversity of wing colors and patterns, often exhibiting Mullerian mimicry. Recent publications of genomes from H. melpomene, H. eratus, and other species has helped localize this color/pattern variation to a handful of genomic regions. The idea that these genes may have co-evolved independently has however been contentious. Hoyal Cuthill and Charleston (2015) address this issue by comparative phylogenetic methods using ten genes across H. melpomene and H. eratus morphs. Their data comprised 127 butterflies from across the radiation, and ~6000 bp of sequences across genes involved in wing color/pattern variation. Population and genic phylogenies were reconstructed and compared revealed (1) single origin of red banding, and blue iridescence within each species, (2) reduced ability to recover phenotypic groupings from neutral makers, and (3) monophyly of H.m.melpomene color genes. Phylogeographic reconstructions suggest that both morphs originated in Amazonia, with added evidences that the adaptive radiation was prompted by Mullerian mimicry than allopatry.
Given the spectacular correspondence between their phenotypes and geographic ranges, it is likely that H. erato and H. melpomene have been major partners in mimicry throughout their evolutionary history. However, wider interactions with other butterfly species, such as Heliconius timareta and Heliconius elevatus, may also have had an influence this mimicry system
Miller et al. 2015 Intraguild predation leads to genetically based character shifts in the threespine stickleback
Banded sculpin feeding on redbelly dace – Image courtesy: https://www.flickr.com/photos/abikeodyssey/4080959043
Threespine sticklebacks (Gasterosteus aculeatus) have been studied extensively, as growing model organisms for recent evolutionary adaptation to changing environments. Miller et al. (2015) study evolutionary response to selection due to intra-guild predation in sticklebacks, and if this response is plastic or with a genetic basis using a common garden experiment in the presence of prickly sculpin (Cottus asper). Individuals from lakes with and without sculpin were grown in a common garden experiment and F1 crosses of the two were used in assessing maternal effects, which were then transferred to two treatment facilities – with and without sculpin, for 36 weeks. Numerous morphological and behavioral characteristics were then measured, and analyzed. Results from wildtype, and common garden sticklebacks indicated that there were several associations with presence or absence of sculpin and measured characteristics – higher armor traits, higher mean vertical position in the water column, decreased shoaling. Several of these characters were also determined to be plastic in marine sticklebacks, with potential maternal effects.
This study provides evidence that intraguild predation leads to evolutionary divergence among stickleback populations (Schluter and McPhail 1992). Phenotypic differences between lakes with and without sculpin have a clear genetic basis. Character shifts have occurred in parallel across replicated populations, therefore these differences are not due to chance.
Further genetic studies are required to characterize these adaptive traits in both species, and understanding how natural selection has contributed to their persistence.
References:
Charleston, Michael. “Wing patterning genes and coevolution of Müllerian mimicry in Heliconius butterflies: support from phylogeography, co‐phylogeny and divergence times.” Evolution (2015). DOI:http://dx.doi.org/10.1111/evo.12812
Miller, Sara E., Daniel Metcalf, and Dolph Schluter. “Intraguild predation leads to genetically based character shifts in the threespine stickleback.” Evolution(2015). DOI:http://dx.doi.org/10.1111/evo.12811