THE INFLUENCE OF DISPERSAL PATTERNS AND MATING SYSTEM ON GENETIC DIFFERENTIATION WITHIN AND BETWEEN POPULATIONS OF THE RED HOWLER MONKEY (ALOUATTA SENICULUS)

Abstract

Abstract. -The relationship between social structure and partitioning of genetic variance was examined in two red howler monkey populations (Wand G) in Venezuela, one of which (G) was undergoing rapid growth through colonization by new troops. Rates and patterns of gene flow had been determined through radiotelemetry and direct observation data on solitary migrants, and 10 years of troop censusing. Standard electrophoresis techniques were used to examine 29 loci in blood samples taken from 137 of the study animals. Analysis of genetic variance demonstrated: (I) a significantly high level of genetic variation among troops within populations (FST = 0.225 for Wand 0.142 for G), and (2) a significant excess of heterozygosity within troops relative to expected (F ,s = -0.136 for Wand -0.064 for G), despite relatively high levels of observed and inferred inbreeding in W. Differences between the populations in F S T values conformed to those predicted based on differences in colonization rate. Comparison of partitioning of genetic variance among different genealogical subsets of troops demonstrated that the pattern of genetic differentiation observed among troops within populations was promoted by an essentially single-male harem breeding structure, a very low rate of random exchange of breeding males among troops, and a high degree of relatedness among troop females. Between-troop genetic differentiation (F sT ) was thereby increased relative to that expected from other types of social organization, while the correlation between uniting gametes within troops (F,s) was decreased. Genetic differentiation between populations (2%) corresponded to that predicted from migration rates. Such a mosaic of genetic variation, combined with differences in reproductive success observed among troops and a high troop failure rate, create conditions in which interdemic selection could result in more rapid spread of advantageous gene combinations than would be expected in a panmictic population, particularly in a colonizing situation in which the founder population is small.

Genetic Variation of Mantled Howler Monkeys (Alouatta palliata) from Costa Rica1

“…This observation contrasts markedly with the high levels of genetic variation shown by howler species from South America (A. seniculus, A. belzebul, and A. fusca;Lima et al 1990, Pope 1992, Sampaio et al 1996. It has been proposed that the low genetic diversity of Central American howlers is due to the action of random genetic drift (Froelich & Thorington 1982, Pope 1996, James et al 1997.…”

“…In addition, A. belzebul was polymorphic for EST, CA2, IDH, and LDH, and A. seniculus was polymorphic for EST, CA2, and MDH (Lima et al 1990, Sampaio et al 1996. Pope (1992) also found that A. seniculus from Venezuela was polymorphic for PGD, ADA, GPI, and two serum proteins (i.e., Tf and an unidentified protein). Contrary to our results, she found that A. seniculus from Venezuela was monomorphic for SOD.…”

“…These findings match the results obtained by Ellsworth (2000) in a comparative study using microsatellite markers. Ellsworth (2000) found that Central American howlers exhibited lower genetic diversity than a small sample of A. seniculus from the site studied by Pope (1992) in Venezuela.…”

“…We would like to paraphrase Froelich and Thorington (1982) and Pope (1996) by stating that the cause for this should be the howler monkeys' unique evolutionary history within the Central American isthmus.…”

“…Under these circumstances, we would expect to find little or no variation within populations. This was the case for the populations described by Malmgren and Brush (1978), Froelich and Thorington (1982), and James et al (1997), and for those reviewed by Pope (1996). At the same time, random genetic drift promotes genetic differentiation between popula-FIGURE 1.…”