Evolutionary Applications 2019;12(7):1385-1401
100-year time series reveal little morphological change following
impoundment and predator invasion in two Neotropical characids
Ilke Geladi, Luis Fernando De León, Mark E. Torchin, Andrew P. Hendry, Rigoberto González, Diana M.T. Sharpe.
Human activities are dramatically altering ecosystems worldwide, often resulting in shifts in selection regimes. In response, natural
populations sometimes undergo rapid phenotypic changes, which, if adaptive, can increase their probability of persistence. However, in many instances, populations fail to undergo any phenotypic change, which might indicate a variety of possibilities, including maladaptation. In freshwater ecosystems, the impoundment of rivers and the introduction of exotic species are among the leading threats to native fishes. We examined how the construction of the Panama Canal, which formed Lake Gatun, and the subsequent invasion of the predatory Cichla monoculus influenced the morphology of two native fishes: Astyanax ruberrimus and Roeboides spp. Using a 100-year time series, we studied variation in overall body shape over time (before vs. after impoundment and invasion) as well as across space (between an invaded and an uninvaded reservoir). In addition, we examined variation in linear morphological traits associated with swim performance and predator detection/avoidance. Notwithstanding a few significant changes in particular traits in particular comparisons, we found only limited evidence for morphological change associated with these two stressors. Most observed changes were subtle, and tended to be site- and species-specific. The lack of a strong morphological response to these stressors, coupled with dramatic population declines in both species, suggests they may be maladapted to the anthropogenically perturbed environment of Lake Gatun, but direct measures of fitness would be needed to test this. In general, our results suggest that morphological responses to anthropogenic disturbances can be very limited and, when they do occur, are often complex and context-dependent.
Evolutionary Applications 2018;12(7):1329-1343
Urbanization erodes niche segregation in Darwin’s finches
Luis F. De León, Diana M. T. Sharpe, Kiyoko M. Gotanda, Joost A. M. Raeymaekers, Jaime A. Chaves, Andrew P. Hendry, Jeffrey Podos.
Urbanization is influencing patterns of biological evolution in ways that are only beginning to be explored. One potential effect
of urbanization is in modifying ecological resource distributions that underlie niche differences and that thus promote and maintain species diversification. Few studies have assessed such modifications, or their potential evolutionary consequences, in the context of ongoing adaptive radiation. We study this effect in Darwin’s finches on the Galápagos Islands, by quantifying feeding preferences and diet niche partitioning across sites with different degrees of urbanization. We found higher finch density in urban sites and that feeding preferences and diets at urban sites skew heavily toward human food items. Furthermore, we show that finches at urban sites appear to be accustomed to the presence of people, compared with birds at sites with few people. In addition, we found that human behavior via the tendency to feed birds at non-urban but tourist sites is likely an important driver of finch preferences for human foods. Site differences in diet and feeding behavior have resulted in larger niche breadth within finch species and wider niche overlap between species at the urban sites. Both factors effectively minimize niche differences that would otherwise facilitate interspecies coexistence. These findings suggest that both human behavior and ongoing urbanization in Galápagos are starting to erode ecological differences that promote and maintain adaptive radiation in Darwin’s finches. Smoothing of adaptive landscapes underlying diversification represents a potentially important yet underappreciated consequence of urbanization. Overall, our findings accentuate the fragility of the initial stages of adaptive radiation in Darwin’s finches and raise concerns about the fate of the Galápagos ecosystems in the face of increasing urbanization.
Proc Biol Sci. 2019 Dec 4;286(1916):20192290.
Temporally varying disruptive selection in the medium ground finch (Geospiza fortis).
Marc-Olivier Beausoleil, Luke O. Frishkoff, Leithen K. M’Gonigle, Joost A. M. Raeymaekers, Sarah A. Knutie, Luis F. De León, Sarah K. Huber, Jaime A. Chaves, Dale H. Clayton, Jennifer A. H. Koop, Jeffrey Podos, Diana M. T. Sharpe, Andrew P. Hendry†, Rowan D. H. Barrett.
Disruptive natural selection within populations exploiting different resources is considered to be a major driver of adaptive radiation and the production of biodiversity. Fitness functions, which describe the relationships between trait variation and fitness, can help to illuminate how this disruptive selection leads to population differentiation. However, a single fitness function represents only a particular selection regime over a single specified time period (often a single season or a year), and therefore might not capture longer-term dynamics. Here, we build a series of annual fitness functions that quantify the relationships between phenotype and apparent survival. These functions are based on a 9-year mark–recapture dataset of over 600 medium ground finches (Geospiza fortis) within a population bimodal for beak size. We then relate changes in the shape of these functions to climate variables. We find that disruptive selection between small and large beak morphotypes, as reported previously for 2 years, is present throughout the study period, but that the intensity of this selection varies in association with the harshness of environment. In particular, we find that disruptive selection was strongest when precipitation was high during the dry season of the previous year. Our results shed light on climatic factors associated with disruptive selection in Darwin’s finches, and highlight the role of temporally varying fitness functions in modulating the extent of population differentiation.
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