There is now unequivocal evidence for global climate change; however, its potential impacts on evolutionary processes remain unclear. Many species have responded to contemporary climate change through shifts in their geographic range. This could lead to increased sympatry between recently diverged species; likely increasing the potential for hybridization. Recently, following a series of warm winters, southern flying squirrels (Glaucomys volans) in Ontario, Canada rapidly expanded their northern range limit resulting in increased sympatry with the closely related northern flying squirrel (Glaucomys sabrinus). This provided the opportunity to test the prediction that contemporary climate change can act as a catalyst creating conditions for the formation of hybrid zones. Following extensive sampling and molecular analyses (nuclear and mitochondrial DNA), we identified the occurrence of hybridization between sympatric G. sabrinus and G. volans .T here was evidence of backcrossing but not of extensive introgession, consistent with the hypothesis of recent rather than historic hybridization. To our knowledge, this is the first report of hybrid zone formation following a range expansion induced by contemporary climate change. This is also the first report of hybridization between North American flying squirrel species.

Climate change induced hybridization in flying squirrels

In social or group living species, members of groups are expected to be affected differentially by competition through the effect of group size (i.e., the “social competition hypothesis”). This hypothesis predicts an increase in the probability of dispersal with increasing size of social groups. At a more mechanistic level and based on the known effects of competition on stress hormone levels, a positive relationship between group size and glucocorticoids of juveniles should be observed. We used a demographic approach to test these predictions on a natural population of the communally rearing and semifossorial rodent—Octodon degus. Burrow systems provide degus with places to rear offspring and to evade stressful thermal conditions and predators. Thus, we predicted dispersal to increase with increasing number of degus per main burrow system used, a measure of habitat saturation in degus. The probability of dispersal increased with increasing number of degus per main burrow system used. Mean fecal metabolites of cortisol in offspring increased, yet not statistically significantly, with the number of juveniles in groups. These results were consistent with a scenario in which competition drives natal dispersal in juveniles in social degus. In particular, competition would be the consequence of high degu abundance in relation to the abundance of burrow systems available at the time of offspring emergence.

The influence of group size on natal dispersal in the communally rearing and semifossorial rodent, Octodon degus

Familiarity with neighbours affects intrusion risk in territorial red squirrels

On the dynamics of rodent social groups.

Social individuals have organized relationships that affect fitness and so a species' tendency to be social has important implications for its population ecology, gene flow, and its distribution in space and time. We quantitatively examined the social structure of southern flying squirrels (Glaucomys volans) and tested for a role of kinship and prior familiarity in predicting social structure. To quantify social structure, we monitored nest group composition of southern flying squirrels. All squirrels at the study site were marked with passive integrated transponder (PIT) tags and nest cavity entrances were monitored with automated PIT tag recorders for a period of 28 months. Squirrels were genotyped at eight microsatellite loci. Permutation tests of associations suggested that individuals nested with other specific individuals more often than expected by chance. The lagged association rate indicated that relationships were stable and persisted across seasons and years. Multiple summer nest associates came together in winter to form larger nest groups which were likely important for social thermoregulation. A measure of prior familiarity, but not kinship, was related to the proportion of time individuals nested together during winter. We suggest that the evolution of sociality in southern flying squirrels is driven largely by mutually beneficial behaviors related to social thermoregulation although other, as of yet, unidentified mechanisms are needed to explain sociality in the warm season. We hypothesize that minimum group size requirements associated with social thermoregulation could explain the absence of this species in patchy landscapes and aspects of range boundary dynamics near their northern range boundary.

Complex social structure of southern flying squirrels is related to spatial proximity but not kinship

Genetic relationships were examined among wild-caught southern flying squirrels (Glaucomys volans) sharing the same natural nest cavity. Under natural conditions, typically 75‐80% of southern flying squirrel nest groups comprise adult-aged individuals. The remainder nest in family-based groups or are solitary. The coefficient of relatedness within nest groups of adult individuals and family-based nest groups was examined through microsatellite DNA analysis. Family or adult nest groups were identified from the age class of individual group members determined through a discriminant function analysis based on body mass. From this information, nest groups were categorized as family-based groups comprising a single adult female with nestlings, adult groups comprising adult aged-individuals, or subadult nest groups. The average coefficient of relatedness was determined in each nest group. Within the putative family groups, most individuals were 1st-order relatives. In the adult nest groups, the coefficient of relatedness was low, indicating that these individuals were unrelated. The relationships within the subadult nest groups were intermediate. This is the 1st study to show that adult nestmate southern flying squirrels typically are unrelated and do not nest in family-based groups.

Kevin S. Laves

Papers

Relatedness within nest groups of the southern flying squirrel using microsatellite and discriminant function analyses