A high level of outcrossing in the vulnerable species Prosopis rubriflora in a Chaco remnant

Prosopis rubriflora Hassl. is a tree species typically found in chaquenian areas, mainly with an arborised phytophysiognomy in the southern region of the Pantanal wetland. This species has become vulnerable in recent decades as a result of considerable increases in anthropogenic activities such as cattle breeding, and this vulnerability has also been observed in several other native species. The goal of this study was to estimate the mating system of P. rubriflora in a Chaco remnant by analysing 10 microsatellite markers. Samples were collected over 2 years (2010–213 seedlings and 2011–180 seedlings), and the results suggest that the mating system of P. rubriflora is preferably allogamous. A progeny array was predominantly composed of half-sibs (from 76 to 79%), full-sibs (from 15%) and self-half-sibs (from 6 to 9%). The outcrossing rate between related individuals was significant in 2011 but not in 2010. The average co-ancestry coefficient () ranged from 0.158 to 0.162, and the variance effective size (Ne) ranged from 3.05 to 3.13. The number of seed trees required for seed collection (m) to retain an effective size of 150 in progeny array samples was 48–49. The high levels of outcrossing of P. rubriflora appear to be related to several mechanisms that avoid selfing and due to the behaviour of native pollinators, which clearly contribute to the gene flow of the species.

On the number of reproductives contributing to a half-sib progeny array

We address various statistical aspects of biological parentage in multi-offspring broods that arise via multiple paternity or multiple maternity and, hence, consist of mixtures of full- and half-sibs. Conditioned on population genetic parameters, computer simulations described herein permit estimation of: (1) the mean number of offspring needed to detect all parental gametes in a brood and (2) the relationship between the number of distinct parental gametes found in a brood and the number of parents. Results are relevant to the design of empirical studies employing molecular markers to assess genetic parentage in polygynous or polyandrous species with large broods, such as are found in many fishes, amphibians, insects, plants and other groups. The utility of this approach is illustrated using two empirical data sets.