Estruturação genética em populações do tangará-dançarino Chiroxiphia caudata (Aves, Pipridae) no corredor costeiro da Mata Atlântica (SP) e sua importância para a conservação.
Resumen
Neotropical passerine birds that inhabit forests understory are thought to
be highly sedentary, which may result in greater genetic differentiation among
populations than in temperate species. The species of the genus Chiroxiphia
(Pipridae) perform highly specialized courtship displays in which males
aggregate at traditional arenas, or ``leks´´, performing a precopulatory dance.
Each lek consists of 2-6 males, where a linear dominance hierarchy exists.
With rare exceptions, the dominant male perform all of the copulations,
resulting in one of the highest variances in male mating success ever
demonstrated in vertebrates. Since subordinate males (beta) expend energy
dancing, increasing the fitness of the alpha male, without receiving any
immediate benefit, it has been hypothesized that kin selection could be
involved, providing a genetic payoff to the subordinate individuals.
Considering that the leks locations are permanent, if kin selection is involved,
male dispersal is expected to be limited at some level, while females, that are
free to visit different leks, would be the more dispersive sex. Sedentariness
associated with the high variance in male mating success, as well as the
possibility of kin selection, make of these birds candidates to present high
levels of interpopulation structuring. In this work we investigated the extent of
variation within and among blue-manakin, Chiroxiphia caudata, populations
using 10 polymorphic microsatellite loci, along a 415 km transect, which
covers most of the extension of the largest remaining continuum of one of the
most endangered ecosystem in the planet, the Brazilian Atlantic forest. Low
but significant levels of differentiation were found across populations (FST = -
0.0002 to 0.023). This structuring must be mostly related to social aspects of
the species, and three non exclusive hypothesis can be urged to explain it: (1)
genetic drift due to the intra population smaller effective population size
caused by the high variance in male mating success; (2) inbreeding if males
contribute to more than one generation of females and (3) the existence of kin
selection among males from the same lek. Besides, an isolation by distance
pattern of differentiation was found, indicating that dispersal is at some level
limited, which can also have contributed to the observed structuring. Thus, a
significant part of the blue manakin genetic diversity was distributed among
populations, even at such a limited geographic scale. When these continuous
areas get disconnect reducing gene flow, these animals are probably much
more prone to suffer inbreeding depression and loose alleles than species that
are not naturally inbred, such as most of the temperate birds. In this scenario,
preserving continuous areas must be essential to maintain the genetic
diversity, and the continuous corridor here studied can be the last large genetic
repository for many Atlantic forest organisms.