Ethology may be related to the genetic structure of a population: Chaetodipus siccus as a study case

Abstract

Philopatry is a biological trait present in a wide variety of zoological taxa. Such conduct is considered as the basis of social behavior among rodents as well as a promoter of spatial distribution of individuals. Females are typically philopatric, thereby they have access to resources to breed offspring. This philopatric tendency is partly responsible of the genetic structuring in the natural populations of mammals. Heteromyid rodents conform complex communities and the agonistic interactions among them are common. Aggressiveness is the way to establish dominance hierarchies. By means of setting a hierarchy, dominant individuals have priority access to critical resources. Chaetodipus siccus is an endemic heteromyid of the Baja California peninsula, distributed on an area of ~270 km 2 , in which a particular pattern of high variation of matrilineal lineages has been observed. That is why it is hypothesized the presence of multiple spatially segregated matrilineal lineages, which are promoted by the aggressive nature of the species, which leads to limited panmixia in the range of C. siccus . To test these hypotheses, it has been conducted a statistically parsimonious haplotype network study using matrilineal markers and behavioral experiments of intra and interspecific dominance. Thirty-four localities were surveyed through C. siccus distribution to capture specimens ( n = 143) for the statistically parsimonious network. Muscle tissue was employed to DNA extraction and fragments of Cytb and COI genes were sequenced. To study intraspecific and interspecific dominance, ethological experiments under different conditions were conducted between females. For this purpose, 52 adult females of C. siccus and five adult females of C. arenarius , C. ammophilus , C. spinatus and C. rudinoris were captured alive and maintained in captivity. Encounters took place inside neutral arenas every other night. Individuals were housed individually inside social cages. Fifty-three haplotypes of Cytb and 15 of COI were identified from 143 individuals of C. siccus . A high variety of private haplotypes were observed (31 for Cytb and 5 for COI). The presence of a dominant individual over another was observed in all conditions of experiments of intraspecific and interspecific dominance. Dominant females were statistically more aggressive than subordinated females ( P < 0.001) even C. siccus dominated the other species. A marked genetic structure is observed, with considerable presence of private haplotypes. It is considered that genetic structure occurs when subpopulations are at least partially isolated from each other. There are no appreciable physical barriers within the range of the species. This is why it is considered that ethological interactions more than geographical features may limit gene flow within the population of C. siccus . Structures with an unusual number of haplotypes in small geographical areas, such as C. siccus , have been previously recognized for other mammal species. It is argued that this pattern is the result of a philopatric character of females; such conduct restricts gene flow between areas. The existence of several matrilineal lineages geographically restricted proposes that females do not disperse, but remain within a very small geographic area. This points directly to the presence of philopatry in females. Agonistic behaviors are the means by which an individual maintains its hierarchy over others, defining its preferential access to resources. For females of C. siccus , its extremely aggressive nature and a territorial behavior have resulted in segregation of matrilineal lineages.