PS 51-45 - Environmental determinants of geographic variation in the occurrence of ant worker polyphenism (Hymenoptera: Formicidae)

Thursday, August 10, 2017
Exhibit Hall, Oregon Convention Center
Frederique La Richeliere, Biology, Concordia University, Montreal, QC, Canada, Ehab Abouheif, Biology, McGill University, Montreal, QC, Canada and Jean-Philippe Lessard, Biology, Concordia University

Ants are ubiquitous in most terrestrial ecosystems and can alter community composition (Hölldobler & Wilson, 1990; Lach, 2009). One of the many interesting facets in the study of ants are the subcastes that workers form – majors, medias and minors. This phenomenon is known as caste or worker polyphenism, which can be defined as the evolution of several phenotypes from a single genotype (Abouheif & Wray, 2002). The development of majors is mediated by nutrition and consequently, juvenile hormone. Once the level of juvenile hormone attains a certain threshold, the developmental program changes for the major program (Wheeler,1991; Lillico-Ouacher & Abouheif, 2017). In Wilson (1968), he noted that there seemed to be a trend for worker polyphenic species to emerge more in the tropics. This seems to align with the productivity hypothesis for species richness, where the most productive environments have the highest species diversity. The main line of inquiry of the present study is to expand on this claim by Wilson (1968) and determine the underlying environmental determinants of worker polyphenic species occurrences. To do so, I have compiled a database of polyphenic and non polyphenic ant species and used publicly available ant occurrence data to examine the distribution of worker polyphenism. The developmental pathways that lead to phenotypic modifications are well known, but the causes for the distribution of caste polyphenic species have not been reviewed in depth.


Previous studies by Wilson (1968) indicate that worker polyphenic ant species are found in the tropics. I replotted the data and estimated the locations of the study sites to re-examine the data. Using Spearman’s correlation, I found that temperature and latitude correlate with higher proportions of worker polyphenism. My preliminary results of the larger data set that I have compiled suggest that temperature, diurnal temperature fluctuation and total ant species diversity are correlated with higher proportions of worker polyphenic species. These preliminary results are an important step towards being able to model spatial occurrences of polyphenic species using environmental variables and phylogenetic history. Ants demonstrate high levels of worker polyphenism and phenotypic plasticity that are influenced by external variables (Rajakumar et al., 2012; Keller & Ross, 1993). Knowing the pattern and underlying mechanisms of this trait allow for a better understanding of large scale evolutionary changes and the ecological consequences.