Fernando Amor

Social and population structure in the ant Cataglyphis emmae.

Dispersal has consequences not only for individual fitness, but also for population dynamics, population genetics and species distribution. Social Hymenoptera show two contrasting colony reproductive strategies, dependent and independent colony foundation modes, and these are often associated to the population structures derived from inter and intra-population gene flow processes conditioned by alternative dispersal strategies. Here we employ microsatellite and mitochondrial markers to investigate the population and social genetic structure and dispersal patterns in the ant Cataglyphis emmae at both, local and regional scales. We find that C. emmae is monogynous and polyandrous. Lack of detection of any population viscosity and population structure with nuclear markers at the local scale suggests efficient dispersal, in agreement with a lack of inbreeding. Contrasting demographic differences before and during the mating seasons suggest that C. emmae workers raise sexuals in peripheric nest chambers to reduce intracolonial conflicts. The high genetic differentiation recovered from the mtDNA haplotypes, together with the significant correlation of such to geographic distance, and presence of new nuclear alleles between areas (valleys) suggest long-term historical isolation between these regions, indicative of limited dispersal at the regional scale. Our findings on the ecological, social and population structure of this species increases our understanding of the patterns and processes involved under independent colony foundation.

Recent speciation and secondary contact in endemic ants

Gene flow is the main force opposing divergent selection, and its effects are greater in populations in close proximity. Thus, complete reproductive isolation between parapatric populations is not expected, particularly in the absence of ecological adaptation and sharp environmental differences. Here, we explore the biogeographical patterns of an endemic ant species, Cataglyphis floricola, for which two colour morphs (black and bicolour) coexist in parapatry throughout continuous sandy habitat in southern Spain. Discriminant analyses of six biometric measurements of male genitalia and 27 cuticular hydrocarbons reveal high differentiation between morphs. Furthermore, the low number of shared alleles derived from nuclear markers (microsatellites) between the morphs at their contact zone suggests the absence of recent gene flow. Mitochondrial DNA (COI) phylogenetic analysis and median‐joining networks show that the black morph is basal to the bicolour morph, with unique haplotypes recovered for each morph. Mismatch distribution analysis and Bayesian skyline plots suggest that they are undergoing different demographic changes, with the bicolour and black morphs at demographic equilibrium and expansion, respectively. Thus, our results show complete reproductive isolation between the two colour morphs as evidenced from genetic, chemical and morphological data. We suggest that these divergence events could be explained by historical vicariance during the Pleistocene, in which reproductive traits experienced strong divergent selection between the morphs initiating or culminating speciation.

Social coercion of larval development in an ant species

Ants provide one of the best examples of the division of labor in animal societies. While the queens reproduce, workers generally refrain from laying eggs and dedicate themselves exclusively to domestic tasks. In many species, the small diploid larvae are bipotent and can develop either into workers or queens depending mostly on environmental cues. This generates a conflicting situation between the adults that tend to rear a majority of larvae into workers and the larvae whose individual interest may be to develop into reproductive queens. We tested the social regulation of larval caste fate in the fission-performing ant Aphaenogaster senilis. We first observed interactions between resident workers and queen- and worker-destined larvae in presence/absence of the queen. The results show that workers tend to specifically eliminate queen-destined larvae when the queen is present but not when she is absent or imprisoned in a small cage allowing for volatile pheromone exchanges. In addition, we found that the presence of already developed queen-destined larvae does not inhibit the development of younger still bipotent larvae into queens. Finally, we analyzed the cuticular hydrocarbon profiles of queen- and worker-destined larvae and found no significant quantitative or qualitative difference. Interestingly, the total amount of hydrocarbons on both larval castes is extremely low, which lends credence on the chemical insignificance hypothesis of larval ants. Overall, our results suggest that workers control larval development and police larvae that would develop into queens instead of workers. Such policing behavior is similar in many aspects to what is known of worker policing among adults.

A year in an ant's life: Opportunism and seasonal variation in the foraging ecology of Aphaenogaster senilis 1

Abstract: Ants are important consumers in most terrestrial ecosystems. They show a great diversity of diets and foraging strategies. Here, we analyzed how circannual variation in resource use by the Mediterranean species Aphaenogaster senilis is related to colony life cycle and resource availability. In southwestern Spain, this species is active almost year-round, but foraging intensity decreases 10-fold between March and November, following larval production. In the summer, ants refrain from foraging at midday to avoid high temperatures. We hypothesized that diet and foraging plasticity could also explain the ecological success of this species. There are several techniques for assessing the diet of ants. Combining isotope analyses with conventional methods can provide better taxonomic resolution of resource utilization. Using a combination of classic and isotopic analyses, we found that 1) the proportion of plant and animal-derived items collected by foragers did not vary significantly from March to November, and 2) isotope analyses indicated a decrease in the trophic level of A. senilis between June and September, suggesting a difference between collected material and items assimilated. Interestingly, most animal prey were collected by individual ants, and many were retrieved alive. Therefore, A. senilis is not only a scavenger, but also a non-negligible predator, particularly of aphids. The abundance of the most common animal-derived items in the diet was proportional to their abundance in the study area. We conclude that A. senilis is an opportunistic species that is able to feed on a variety of resources, which may be key to its ecological success.

Frequent colony orphaning triggers the production of replacement queens via worker thelytoky in a desert-dwelling ant

Although related, Cataglyphis floricola and Cataglyphis tartessica show very different responses to colony orphaning. In the laboratory, under queenless conditions, C. tartessica workers produced male offspring via arrhenotoky, while C. floricola workers produced female offspring, including new queens, via thelytoky. Both species have workers with active ovaries that produce trophic eggs. In the field, in the late spring, C. floricola colonies were more likely to be orphaned than were C. tartessica colonies, probably due to differences in how they performed fission, their colony foundation system. The combined action of these two features could explain the presence of thelytoky in C. floricola and its absence in C. tartessica.

Nutritional versus genetic correlates of caste differentiation in a desert ant

1. In many ant species, caste differentiation stems from trophic differences at the larval stage. Adult workers that feed larvae have great control over the allocation of colony resources to growth (production of workers) versus reproduction (production of queens). However, larval caste fate may also be constrained very early on through direct genetic effects or non‐genetic maternal effects.

Origin and distribution of desert ants across the Gibraltar Straits

The creation of geographic barriers has long been suspected to contribute to the formation of new species. We investigated the phylogeography of desert ants in the western Mediterranean basin in order to elucidate their mode of diversification. These insects which have a low dispersal capacity are recently becoming important model systems in evolutionary studies. We conducted an extensive sampling of species belonging to the Cataglyphis albicans group in the Iberian Peninsula (IP) and the northern Morocco (North Africa; NA). We then combined genetic, chemical and morphological analyses. The results suggest the existence of at least three and five clades in the IP and NA, respectively, whose delineation partially encompass current taxonomic classification. The three Iberian clades are monophyletic, but their origin in NA is uncertain (79% and 22% for Bayesian and Maximum Likelihood support, respectively). The estimation of divergence time suggests that a speciation process was initiated after the last reopening of the Gibraltar Straits ≈5.33 Ma. In the IP, the clades are parapatric and their formation may have been triggered by the fragmentation of a large population during the Pleistocene due to extended periods of glaciation. This scenario is supported by demographic analyses pointing at a recent expansion of Iberian populations that contrasts with the progressive contraction of the NA clades. Niche modeling reveals that this area, governed by favorable climatic conditions for desert ants, has recently increased in the IP and decreased in NA. Altogether, our data points at geoclimatic events as major determinants of species formation in desert ants, reinforcing the role of allopatric speciation.