My research centers on three main areas:
(1) The evolution and maintenance of colour polymorphisms in warning coloration
(2) Rapid evolution
(3) Sex linkage and adaptation.
To study them, I use a combination of field, laboratory, mathematical, and behavioural experiments. I have two main study systems: the wood tiger moth Arctia plantaginis, and the Trinidadian guppy Poecilia reticulata. My research is interdisciplinary and involves collaborations with multiple molecular and theoretical biologists.
The Maintenance of Colour Polymorphism in Warning Coloration
Aposematic organisms use conspicuous or distinctive markings to warn predators of their general toxicity, unpalatability, and/or unprofitability. The advantage of a highly recognizable warning signal that allows efficient predator learning should select for the most common coloration and thus lead to monomorphism, yet there are many polymorphic aposematic species. Solving the riddle of polymorphism in such challenging cases would therefore represent an important advance in our understanding of the maintenance of trait polymorphisms in general.
The wood tiger moth Arctia plantaginis: The predator avoidance and evolution of the wood tiger moth has been studied extensively (e.g. Ojala et al. 2007, Lindstedt et al. 2011, Nokelainen et al. 2013, 2014, Galarza et al. 2014, Gordon et al. 2015b). A. plantaginis is aposematic and polymorphic in its adult form: Female hindwing coloration ranges continuously from red to orange and Male wood tiger moths exhibit discrete and hindwing morph coloration on a broad geographical scale. Both larvae and adult moths are unpalatable to predators (Lindstedt et al. 2011) and current unpublished data suggests that the adult moths synthesize the chemicals de novo (Burdfield-Steel et al. Unpublished). My research mainly focuses on the maintenance of male hindwing polymorphism (below pictures (1) setting up large scale outside enclosure mating experiment and (2) male and female moth mating pair).
Past research has shown that the more conspicuous yellow male moths have greater signal efficacy, and hence higher survival against predators (Nokelainen et al., 2012). On the other hand, white male moths generally have a mating advantage over the yellow morph, mainly under high densities (Nokelainen et al. 2012) and frequencies (Gordon et al. 2015b; Rojas, Gordon, and Mappes 2015). However, a recent model shows that this trade-off between sexual and natural selection is still not enough to maintain morph coexistence at the high frequencies we observe across the globe (Gordon et al. 2015b). Instead, it is likely that there are other factors that have a combined influence with either natural and/or sexual selection leading to the variation in warning signaling we see in nature.
I examine these other factors using a variety of experiments. For example, in collaboration with Dr’s Johanna Mappes, Bibiana Rojas, Juan Galarza, and Andrés Lopez Sepulcre we perform yearly capture-mark recapture experiments in a wild Finnish population studying their population dynamics, movement patterns etc., with the goal being to later expand to other populations of known varying morph frequencies.
I also examine whether a tradeoff between natural and sexual selection can also drive the evolution and maintenance of colour polymorphism via multiple mating and predation laboratory and semi-wild large-scale enclosure experiments (Gordon et al. 2015c, Rojas, Gordon, and Mappes 2015, Gordon et al. In review).
Finally, I also use the results from the above experiments to parameterize models that study the relative importance of gene flow, habitat heterogeneity, FDS predation pressure, FDS mating success, and genetic linkage on polymorphism. Such empirical parameterizations of the evolutionary process accounting for multiple interacting selective forces throughout the life-history of populations, as opposed to studies on single mechanisms, are rare.
Rapid Evolution
Understanding how organisms evolve to changing environments is fundamental to developing an efficient response to our current biodiversity crisis. For example, some introduced species are often initially restricted in their new environments, but then abruptly proliferate to become invasive pests. This change may be caused by the ability of the invader to quickly evolve new adaptations after establishment. I have been using two large-scale introductions of the rapidly evolving Trinidadian guppy to examine two objectives.
The Trinidadian guppy Poecilia reticulata
Guppies inhabit small freshwater streams in Trinidad in what has been described by some as a natural experiment. In the Northern range mountains of Trinidad, rivers are arranged in parallel flowing both to the north and south slope of the mountain range, providing convenient replication and allowing testable predictions regarding evolutionary change across rivers.
In each river, guppy habitats are separated by barrier waterfalls which block large predators from getting to the more upstream environments, called low predation environments.
Adaptive divergence to differences in predation has led there to be two basic eco-types of guppies: high versus low-predation. Genetic research shows that low-predation populations are derived from high-predation ones. Additionally, various translocations of guppies from high into low-predation environments show rapid adaptive divergence in a variety of morphological, behavioural, and life history traits.
My MSC research first asked whether rapid adaptation to new environments influence major fitness components such as survival. We did this in a variety of steps. We initially introduced guppies from one environment (high predation) into two others (low and high predation) in a different river, and waited for 13-26 generations for possible adaptation. We then documented the adaptive divergence of key life history, morphological, and behavioural traits (Karim et al. 2007; Weese et al. 2010; Easty et al. 2011). Finally, we competed the ancestral population with both introduced populations in their environment and documented that survival itself improved with adaptation to the new environments (Gordon et al. 2009).
Second, we showed rapid evolutionary change of male coloration in guppies (approximately 3 generations after introduction from one high predation environment into two low-predation tributaries in the same stream) where we tracked the evolutionary response as well as individual-based measures of selection (Gordon et al. 2015a).
Future and current work on this topic include:
- Study of evolutionary trajectories and their repeatability. Understanding short-term evolutionary responses requires understanding the factors determining small-scale seasonal and inter-annual fluctuations, which are rarely considered.
- Testing predictive models of the effects of evolution using estimates of heritability, selection, and trade-offs from the introduction data sets.
- Examining behavioural changes in sexual displays and mating in the latest introduced guppies
Sex Linkage
Adaptation requires both inheritance and selection. Most studies in rapid evolution, however, ignore heritability and concentrate on selective pressures or assume a particular mode of inheritance. Little attention is paid to variation in the mode of inheritance itself. Theory suggests that the sex-linkage of sexually-selected traits can influence evolutionary rates. In this research, I again use Trinidadian guppies to empirically examine, in nature, the ecological versus genetic factors (in terms of sex-linkage) that contribute to the evolution of guppy coloration.
The most novel and remarkable finding was that not only does male coloration evolve rapidly in response to a change in selection, but so does its degree of sex linkage (as males evolve more colour, they lose Y-linkage) (Gordon et al. 2012 (F1000 Recommended); Gordon et al. 2017). Current work in this section involves the development of quantitative genetic models to partition the evolutionary response into its sex-linked components, in order to estimate selection on different types of inheritance by relating each’ contribution to fitness.
Thank you for your interest!
Swanne Gordon 