THE MATING SYSTEM OF THE GREATER RHEA: ROLE CHANGE AND PROMISCUITY

MARTELLA, M.B.

Congreso; Reunión Conjunta de las Sociedades de Biosciencias; 2017

Socieades de Biosciencias Argentinas

The Greater Rhea (Rhea americana) is a near threatened ratite whose wild populations are decreasing and exhibit low polymorphism levels. The mating system of this flightless bird is complex, simultaneous polygyny and serial polyandry, and very infrequent among vertebrate species, in which several females copulate with different males and lay their eggs in communal nests. The male constructs the nest, fully incubate the eggs and care for the precocial chicks. Here we evaluated the degree of relatedness among and within broods, with the aim of enlightening the reproductive system of rheas from a genetic point of view. We sampled feathers from 145 nestlings and three males that incubated in 5 nests in the wild. The genotype was determined by means of eight microsatellites developed for rheas, while relatedness was analyzed with software Colony. The study revealed that there were multiple progenitors per nest (14,8 females and 11,2 males). On average, a given female laid in 1,9 nests and produced 3,7 nestlings, while each male had descendants in 1,75 nests and produced 4,5 chicks. Two males were the major two male progenitors in the clutch they incubated (28,6% and 34,5% of the chicks were of their own), whereas the third analyzed male had no descendants, neither in his nest nor in the other ones. Each male successfully mated 3,4 females (range: 1-8), while each female had 2,8 partners (range: 1-5). Most adults (81%) that share descendants in a nest were unrelated, and females were always less related than males. Although most full-sibs occurred within the same nest, both full and half-siblings corresponded to less than 5,5% of all paired comparisons among all chicks (complementary, 94,5% were unrelated). Our study shows that: (i) there are several progenitors of descendants in each nest; (ii) no male that incubate is the progenitor of the majority of chicks in a nest; (iii) not all incubating males leave progeny; and (iv) females do not constitute cohesive and stable groups that lay eggs in the same successively nests. This promiscuous strategy could be preventing further losses of genetic variability, counterbalancing detrimental effects that an impoverished genetic pool can exert on the viability of populations.