“As with mariners shipwrecked near a coast, it would have been better for the good swimmers if they had been able to swim still further, whereas it would have been better for the bad swimmers if they had not been able to swim at all and had stuck to the wreck.” (Darwin 1859)
Above: Chorthippus cazurroi (Bolívar, 1898) is a grasshopper that inhabits the summits of the eastern Cantabrian Mountains (Spain); photograph by Eva de Mas.
This metaphor, although in quite a different context, nicely introduces our paper on mountain organisms (Laiolo et al. 2023). In mountaintops, local conditions — strong winds, chilling temperatures — are hardly suitable for flying, especially for small ectotherms. Given that resources are limited, it would be more advantageous to invest in other traits and process rather than in wings and dispersal. In our study we have found that grasshoppers and bumblebees have progressively shorter wing span from lowlands to mountaintops. This reduction is especially marked in grasshoppers, with many flightless species inhabiting high elevations (Fig. 1). The resources saved from wings are partly invested in other life-history traits: eggs get larger, at the advantage of offspring survival.
The grasshopper Podisma carpetana is endemic to Central and Northern Spain and only inhabits mountainous areas. The male (in this picture) and the female have vestigial wings and do not fly. Photo by Eva de Mas.
This result illustrates the adaptations that two phylogenetically distant insect groups (Orthoptera and Hymenoptera) have evolved. Nonetheless, wings serve to disperse, and the dispersal limitations of highland insects have consequences for populations and communities. This limitation affects alpha and beta diversity, and reduces the interchange of species between peaks but not that from lowlands to peaks. As the climate warms, mountain habitats could rescue species from lower elevations, as these species are like Darwin’s “good swimmers”. A nearby mountain, however, cannot rescue a mountaintop species, since peak-to-peak rescues assume that the species can get there, and these are “stuck to the wreck”. Therefore, the fate of these species depends on other mechanisms, such as persistence in climatic refugia or evolution.
Editors’ choice article: (Free to read online for two years.)
Laiolo, P., Illera, J. C., & Obeso, J. R. (2022). Stuck on top of a mountain: Consequences of dispersal limitations for alpine diversity. Journal of Biogeography 50:282-290. https://onlinelibrary.wiley.com/doi/10.1111/jbi.14513
Our main aim was to determine to what extent mountains are true islands for the organisms that inhabit them. We highlighted a powerful influence of the elevation gradient in individual wing variation, and in the strength of environmental filters. We linked trait-based processes at the species level to emergent features of communities, such as alpha and beta diversity, and their spatial patterns, connecting evolutionary, ecological and biogeographic theory.
A view of Cantabrian Mountain peaks emerging from a sea of clouds. Photo by Paola Laiolo.).
In the end, at least for these insects, are the tops of mountains true islands? We cannot say they are, as they receive immigrants from the sea (the valleys). However, insect populations up there do live isolated by a sea of air … or of water vapor.
Biodiversity Research Institute (Spanish National Research Council, University of Oviedo, Principality of Asturias), Spain
One thought on “Poor flyers in the sky (-islands)”
En los quironómidos la adaptación incluye especies braquipteras y Soteras que eclosionan cuando hay nieve y copulan sobre ellallehando a más de 4000 metros en el Himalaya