Yours, mine and ours: The strange breeding biology of Rheas

MARTELLA MB,; NAVARRO JL

Berlín

Conferencia; Conferencias de Investigadores Invitados; 2017

Leibniz Institute for Zoo and Wildlife Research (Leibniz IZW)

The Greater and the Lesser Rhea are iconic species of the regions where they are distributed (Pampas, Patagonia and Puna), and they are the largest birds in South America. These conspicuous animals have been an object of curiosity of explorers, peregrines, adventurers, and naturalists that have visited South America since the 1600´s. Their reproductive biology was firstly described in a gross manner in several works of the XVII and XVIII centuries. Although slightly more detailed information was provided later, until the 1960´s most of it was still anecdotal and hearsay. Thereafter reproductive behavior and social structure were progressively better reported with more scientific basis. Nevertheless, some inadequately described features of the reproductive biology of rheas were incorporated into various considerations of the evolution of reproductive behavior patterns, and there was the danger of assuming the status of fact through repetition. In the early 2000´s the stated features of the breeding system of these birds were that there exist: reproductive group formation and defense, simultaneous polygyny, serial and probably simultaneous polyandry, and communal nesting. It was also known that the male builds the nest, fully incubates, cares for the precocial chicks, and even adopts others´ chicks.Despite this apparent plethora of information, there were several important questions on the reproduction of rheas still to be answered by means of original scientific research, such as: (1) Is simultaneous polyandry rare or is it common?; (2) Are the reproductive groups of females cohesive (members copulate with the same male and lay their eggs in same successive nests) throughout the reproductive season?; (3) Do those non-incubating males produce any offspring?; (4) Is the incubating male the progenitor of all, some, or none of those chicks he hatches? Is he only a ?helper??; (5) What is the relatedness of those chicks coming from the same nest?; (6) What is the relatedness among parents (within and between genders) of chicks coming from a communal nest?; and (7) What could be the evolutionary cause of adoption?We started a DNA genotyping study to enlighten the parentship and relatedness within and among broods to clarify the genetic reproductive system of Rheas. We collected five complete clutches and feathers from three incubating males in a population from central Argentina. The eggs were artificially incubated, and the DNA from feathers of the 145 chicks produced was extracted. Genotyping was determined for eight microsatellite loci developed for rheas, and sibship analysis was conducted. Our preliminary results showed that: there were a larger number of progenitors than it was originally thought involved in the brood of a given nest; those incubating males with the larger percentage of paternity in their brood were father of less than 40% of the chicks; an incubating male was not progenitor of any chick, neither within the brood in his nest nor in the other sampled nests; most adults sharing progeny in the same nest were potentially unrelated, and females were always less related than males; full-sib chicks occurred within nests, but both full-sib and half-sib relationships represented a very small portion of all paired comparisons among all chicks, what means that most of the paired comparisons revealed unrelated chicks.We can conclude that there are several progenitors of both sexes within a clutch, the incubating male is not the progenitor of the majority of the chicks produced in his nest, incubating males could even have no progeny at all (?helper?), and females did not constitute a cohesive group laying their eggs in the same nests. This promiscuous strategy seems to counterbalance the low genetic variability rates detected in this species. Further research is needed to answer at least these two questions: do the birds from a given winter flock reunite in the following winter, or do neighboring birds mix significantly? What is the survival rate of adults? Also, there is the need for stronger evidence of parenthood in wild populations, and of more precise data for developing better models of population dynamics of rheas in the wild. Therefore, we propose that the next research actions should be focused on these topics.