Gene Flow and Hybridization between Numerically Imbalanced Populations of Two Duck Species in the Falkland Islands

Abstract

Interspecific hybridization is common in plants and animals, particularly in waterfowl (Anatidae). One factor shown to contribute to hybridization is restricted mate choice, which can occur when two species occur in sympatry but one is rare. The Hubbs principle, or “desperation hypothesis,” states that under such circumstances the rarer species is more likely to mate with heterospecifics. Here we report interspecific hybridization between two waterfowl species that coexist in broad sympatry and mixed flocks throughout southern South America. Speckled teal (Anas flavirostris) and yellow-billed pintails (Anas georgica) are abundant in continental South America, but in the Falkland Islands speckled teal outnumber yellow-billed pintails approximately ten to one. Using eight genetic loci (mtDNA and 7 nuclear introns) coupled with Bayesian assignment tests and relatedness analysis, we identified a speckled teal x yellow-billed pintail F1 hybrid female and her duckling sired by a male speckled teal. Although our sample in the Falkland Islands was small, we failed to identify unequivocal evidence of hybridization or introgression in a much larger sample from Argentina using a three-population “isolation with migration” coalescent analysis. While additional data are needed to determine if this event in the Falkland Islands was a rare singular occurrence, our results provide further support for the “desperation hypothesis,” which states that scarcity in one population and abundance of another will often lead to hybridization.

Crossing species boundaries : the hybrid histories of the true geese

“…In the Falkland Islands, Speckled Teals (Anas flavirostris) outnumber Yellow-billed Pintails (Anas georgica) about ten to one. This numerical imbalance can explain the asymmetrical gene flow from Yellow-billed Pintail into Speckled Teal (McCracken and Wilson, 2011). Similar cases have been described for Mallard and Eastern Spot-billed Ducks in Eastern Russia (Kulikova et al, 2004) and Streptopelia doves in Uganda (den Hartog et al, 2010).…”

“…Another good example of the Desperation Hypothesis concerns two duck species on the Falkland Islands, where Speckled Teals (Anas flavirostris) outnumber Yellow-billed Pintails (Anas georgica) about ten to one. This numerical imbalance leads to hybridization (McCracken and Wilson, 2011). The Desperation Hypothesis is not restricted to natural situations, in captivity birds are often confronted with a scarcity of conspecifics and might choose to mate with the available heterospecifics.…”

“…The recent developments in avian genomics offer opportunities to quantify levels of recent and ancient gene flow (Kraus and Wink, 2015, Jarvis, 2016, Toews et al, 2016 and to reconstruct the evolutionary history of a syngameon. For example, many studies have quantified the amount of recent gene flow between certain species pairs in the genus Anas (McCracken and Wilson, 2011, Guay et al, 2015, and see studies on Mallard hybridization listed above) and several studies suggested high levels of ancient gene flow in this genus (Kraus et al, 2012, Lavretsky et al, 2014, Peters et al, 2014b.…”

“…The incidence of hybridization varies among bird orders with Anseriformes (waterfowl: ducks, geese and swans) showing the greatest propensity to hybridize. The study of waterfowl hybridization is biased towards ducks, as exemplified by an extensive inventory of hybrid ducks (Gillham and Gillham, 1998), an analysis of hybrid duck fertility patterns (Tubaro and Lijtmaer, 2002) and various genetic studies on introgressive hybridization (Kraus et al, 2012, Lavretsky et al, 2016, Peters et al, 2014a, McCracken and Wilson, 2011. The knowledge on goose hybridization is clearly lagging behind.…”

Migration-Selection Balance Drives Genetic Differentiation in Genes Associated with High-Altitude Function in the Speckled Teal (Anas flavirostris) in the Andes

“…The α A -hemoglobin subunit (676 bp; HBA2), β A -hemoglobin subunit (1,578 bp; HBB), and mitochondrial sequences containing part of the control region and tRNA-Phe gene (McCracken and Wilson 2011) were obtained from GenBank, for the same 20 individuals that were used in this study (McCracken et al. 2009a), except for the high-altitude population, for which the mitochondrial sequences had not been published previously (NCBI accession numbers are provided in supplementary table S2, Supplementary Material online).…”