Claire Marie Soleil Dufour

Comprendre les mécanismes évolutifs permettant la persistance des populations face aux changements environnementaux est au centre des préoccupations tant scientifiques que sociétales, de par l'anthropisation grandissante. L'étude i) de la diversification des espèces dans des environnements contrastés et ii) de la coexistence entre ces espèces permet d'appréhender ces mécanismes. En effet, la coexistence entre espèces, et donc leur persistance, dépend de leur niveau de divergence, tant sur des caractères écologiques que reproducteurs. Les études empiriques présentées dans cette thèse portent sur la divergence de deux espèces soeurs chez la souris striée africaine : Rhabdomys bechuanae et Rhabdomys dilectus dilectus. La rencontre entre les deux distributions spécifiques dans un même macro-environnement m'a permis d'étudier la complexité des mécanismes de divergence et de coexistence à fine échelle. Pour cela, les réponses des espèces face à l'hétérogénéité environnementale et à l'interférence spécifique ont été étudiées sur 4 dimensions de la niche : i) la sélection d'habitat, ii) le comportement spatial, iii) le régime alimentaire et iv) le comportement social ainsi que sur le système de reconnaissance sexuelle. Les principaux résultats soulignent l'importance de la prise en compte des différentes dimensions de la niche et de leurs interactions dans l'étude de la divergence et de la coexistence. En effet, alors que la divergence entre les espèces est principalement caractérisée par une évolution en allopatrie de la sélection d'habitats et du système de reconnaissance sexuelle, la plasticité des comportements alimentaires et sociaux reflète la réponse des organismes à l'hétérogénéité spatio-temporelle de l'environnement. La réponse des espèces à l'interférence spécifique est, quant à elle, principalement due à la plasticité des comportements spatiaux (taille et chevauchement des domaines vitaux). Cette thèse se clos par une discussion sur l'apport de ces études micro-évolutives, tenant compte de la complexité des mécanismes de divergence et coexistence, à la compréhension des processus évolutifs à plus large échelle : lors de la radiation écologique d'un genre.

Spatial and social population structures can influence intra- and interspecific genetic processes. We investigated the spatial and social genetic structure of two sister species and evaluated whether there was evidence of hybridisation between them at a microgeographic scale, in syntopy. Our study models were Rhabdomys bechuanae (Rbech) and Rhabdomys dilectus dilectus (Rdil). We generated population genetic data using microsatellite markers and cross-referenced some of these results with published behavioural data from a prior study, reanalysed here. We compared genetic diversity and gene flow both in sympatry and allopatry, we tested for hybridisation between the sister species in sympatry and assessed the relationship between kinship and fine-scale spatial and social organisation. Genetic diversity was high within all populations of the two species. Population genetic substructure was more pronounced in Rbech than in Rdil, consistent with stronger group cohesion reported for Rbech. STRUCTURE and NEWHYBRIDS analyses suggested that sympatric individuals, 5% in Rbech, and 2% in Rdil, might have hybrid ancestry. Our results indicate social fences may limit gene flow within and between species. Further, limited hybridisation suggests that, despite syntopy, only rare events of hybridisation may occur, possibly at phases of density troughs and/or that F1 hybrids have a relatively low fitness.

During the last two decades, genotyping of African rodents has revealed important hidden diversity within morphologically cryptic genera, such as Rhabdomys. Although the distribution of Rhabdomys is known historically, its diversity has been revealed only recently, and information about the distribution range of its constituent taxa is limited. The present study contributes to clarifying the distribution of Rhabdomys taxa, primarily in southern Africa, and identifies gaps in our knowledge, by: 1) compiling the available information on its distribution; and 2) significantly increasing the number of geo-localised and genotyped specimens (n = 2428) as well as the localities (additional 48 localities) sampled. We present updated distribution maps, including the occurrence and composition of several contact zones. A long-term monitoring of three contact zones revealed their instability, and raises questions as to the role of demography, climate, and interspecific competition on species range limits. Finally, an analysis of external morphological traits suggests that tail length may be a reliable taxonomic trait to distinguish between mesic and arid taxa of Rhabdomys. Tail length variation in Rhabdomys and other rodents has been considered to be an adaptation to climatic (thermoregulation) and/or to habitat (climbing abilities) constraints, which has still to be confirmed in Rhabdomys.

Invasive species are a world‐wide threat to biodiversity. Yet, our understanding of biological invasions remains incomplete, partly due to the difficulty of tracking and studying behavioural interactions in recently created species interactions. We tested whether the interactions between the recently introduced invasive lizard Anolis cristatellus and the native Anolis oculatus in Dominica have led to changes in species recognition and aggressive behaviour of the native species. The use of realistic robots allowed us to test the behavioural response of 131 A. oculatus males towards relevant and controlled conspecific versus heterospecific stimuli, directly in the field and in two contexts (allopatry vs. sympatry). Our results show that species recognition evolved prior to sympatry in A. oculatus. Moreover, interspecific competition resulted in an increase in the time spent displaying and a divergence in the aggressive behaviour of the native species towards conspecifics versus heterospecifics. Inherent species recognition and higher aggressive behaviour may limit species coexistence as they are expected to favour A. oculatus during territorial interactions with A. cristatellus. While more studies are needed to understand the causes of these behavioural shifts and their consequences on long‐term species coexistence, the present study highlights the role of behaviour as a first response to interspecific interactions.

Nest‐site selection is an important component of species socio‐ecology, being a crucial factor in establishment of group living. Consequently, nest‐site characteristics together with space‐use proxies may reveal the social organization of species, which is critical when direct observation of social interactions is hindered in nature. Importantly, nest‐site choice is expected to be under strong selective pressures and the object of intra‐ and interspecific competition. Although the bulk of research on sociality focuses on its ecological drivers, our study introduces interspecific competition as a potential factor that could influence social evolution. We investigated the influence of habitat and interspecific competition on the social organization of two sister species of the African four striped mouse, Rhabdomys dilectus dilectus and Rhabdomys bechuanae , in a similar macroenvironment. These species diverged in allopatry and occupy distinct environmental niches. We radiotracked 140 adults to identify their nest‐sites, determine nest characteristics and record groups that shared nest‐sites. Group cohesion was estimated from nest‐site fidelity, group association strength, and home range overlap within versus between group members. We compared the two species in sympatry versus parapatry to determine the impact of species interference on sociality. In parapatry, the two species selected distinct nest‐site types, interpreted as different anti‐predator strategies: R. bechuanae selected fewer, spaced, less concealed nest‐sites whereas R. d. dilectus selected clumped and less visible nest‐sites. Rhabdomys bechuanae also showed more cohesive and stable social groups than R. d. dilectus . In sympatry, compared to R. bechuanae , R. d. dilectus occupied similar nest‐sites, however slightly more exposed and clumped, and displayed similar nest‐site fidelity and group association strength. We conclude that although habitat selection may be an important driver of social divergence in Rhabdomys , species interference, by limiting R. d. dilectus movements and forcing nest‐site sharing may induce new ecological pressures that could influence its social evolution.

Invasive species are a global threat to biodiversity. Cases where the invasion has been tracked since its beginning are rare, however, such that the first interactions between invasive and native species remain poorly understood. Communication behavior is an integral part of species identity and is subject to selection. Consequently, resource use and direct interference competition between native and invasive species may drive its evolution. Here, we tested the role of interactions between the recently introduced invasive lizardAnolis cristatellusand the nativeAnolis oculatuson variation in behavior and communication in Calibishie (Dominica). From May to June 2016, we filmed 122 adult males of both species displaying in banana farms under two contexts (allopatry and sympatry). We then recorded (i) the proportion of time spent displaying and (ii) the relative frequency of dewlap vs. push-up displays. To control for habitat variation, we measured and compared the habitat characteristics (canopy openness and habitat openness) of 228 males in allopatry and sympatry. While the habitat characteristics and total display-time did not differ between the contexts for the two species, the proportion of display-time spent dewlapping byA. cristatellusdecreased in sympatry. The display ofA. oculatusdid not differ between the contexts, however. Shifts in microhabitat use, predation pressure, or interspecific interference are potential factors which might explain the behavioral changes in display observed inA. cristatellus. This study highlights the role of behavioral traits as a first response of an invasive species to recent competition with a closely related native species.

Species invasions are a global scourge. Nonetheless, they provide the appropriate evolutionary setting to rigorously test the role that interspecific competition plays in species evolution. The process of ecological character displacement, in which species diverge in sympatry to minimize resource use overlap, is one example. Here, we examine whether ecological character displacement occurs as the result of a species invasion and, if so, whether morphological adaptations subsequently evolve. We studied the invasion of the lizard Anolis cristatellus in Dominica, where the native Anolis oculatus occurs, and compared nine allopatric and 11 sympatric populations at two scales: across the island, where A. cristatellus invaded since 1998, and in the northeastern region (Calibishie), where the species arrived in 2014. Perch height and diameter, as well as body, limb and toepad traits, were measured on 593 adults. In sympatry, habitat divergence occurred rapidly but was associated with morphological divergence at the island scale only: A. oculatus perched higher and possessed shorter limbs, while A. cristatellus moved downward with associated longer limbs and, in females, fewer toepad lamellae. The different results for the two scales suggest that sympatry is too recent at Calibishie for morphological trait evolution to occur.

This study reports a high rate of ventro–ventral (VV) copulation in 2 species of the African four-striped mouse—Rhabdomys—and explores its causes. VV postures were observed in 67% encounters with mating attempts, in both species and during intra- and interspecific trials, although discrimination between the species occurred (i.e., duration of sexual behavior or social investigation varied between intra- and interspecies encounters). Striped mice displayed more investigatory behavior during encounters with VV coitus postures than during encounters without mating attempts or with only dorso–ventral postures. Furthermore, mating solicitation was greater in females than in males exclusively when VV coitus occurred, suggesting that females’ initiative could explain the high rate of VV postures in our model organism. We propose different hypotheses among which the role of pleasure through its supposed direct and indirect adaptive implications in triggering female initiative.