Crested Duck Lophonetta specularioides

  • Order: Anseriformes
  • Family: Anatidae
  • Polytypic: 2 subspecies
  • Authors: Mariana Bulgarella
Sections

Systematics

Geographic Variation

Two described subspecies. Subspecies designations have been based on morphological and plumage differences, and confirmed by molecular analyses (Bulgarella et al. 2012). L. s. specularioides has a red iris, smaller body size, and more brownish or blackish mottled plumage, whereas L. s. alticola possesses a yellow-orange iris, larger body size, and more uniform, washed out plumage with fewer breast spots (Phillips 1922−1926).

Overall body size of crested ducks differs between the two subspecies and between the sexes (Bulgarella et al. 2007). Male and female L. s. alticola are significantly larger than male and female L. s. specularioides. Larger bodied individuals are found at higher elevations in the Andes (3000–5000 m), with the coastal and inland specimens from Patagonia being smaller, and the Mendoza specimens being intermediate in size between the two populations.

Morphologically intermediate populations of crested ducks, such as those found in Mendoza, Argentina, might be interpreted as evidence for introgression between the two populations, i.e., Andean Crested Ducks in the north and Patagonian Crested Duck populations in the south (Navas and Bo 1998). Intermediate morphology might also be maintained by natural selection on body size of individuals locally adapted to inhabiting intermediate elevational environments.

Analysis of multilocus genetic variation revealed a significant pattern of genetic differentiation between lowland and highland populations of Crested Ducks. The FST values for six autosomal reference loci were consistent with a model of neutral evolution. Historical migration rates based on the joint estimate for the six introns averaged 2.6 effective migrants ⁄ generation into the highlands from the lowlands. By contrast, no migration was observed into the lowland population from the highlands following population divergence (Bulgarella et al. 2012).

Geographic analysis of gene flow documented a strong pattern of haemoglobin differentiation in the distinct environments that crested ducks inhabit. The mismatch in migration estimates between the globins and the autosomal introns likely reflect the more restricted movement of haemoglobin alleles along the elevational gradient relative to the neutral nuclear alleles. Four derived amino acid polymorphisms occurred at high frequencies in the highland population, whereas the lowland population generally lacked these alleles and was predominantly fixed for the ancestral haemoglobin alleles (Bulgarella et al. 2012).

Geographic variation in nuclear DNA was strikingly similar to the variation in morphometrics previously reported in Bulgarella et al. (2007). In the molecular analysis, we found reciprocally monophyletic lineages in mtDNA and diagnosable multilocus genotypes between highland and lowland populations. Furthermore, individuals from Mendoza were intermediate in size in the morphological study. Likewise, multilocus data indicated that Mendoza individuals carried a mix of highland and lowland genotypes (including individuals with admixed ancestry), suggesting that the two morphotypes interbreed within that region. These concordant results between mtDNA, nuclear DNA, and morphology indicate that Crested Ducks comprise at least two genetic populations, corresponding to subspecies designations, but that some gene flow occurs between them (Bulgarella et al. 2012).

Related Species

This section is based on Bulgarella et al (2010).

Johnson and Sorenson (1998, 1999) were the first to recognize the shared ancestry of Amazonetta, Speculanas, Lophonetta, and Tachyeres (the South American duck clade). Later, the phylogenetic relationships among these genera were revised using a multilocus analysis approach. The monophyly of the four South American duck genera and their relationship to the dabbling ducks is strongly supported in diferent analyses with a set of 23 outgroup taxa (5 representative Anas dabbling duck species and 18 other waterfowl genera). Bayesian posterior probability and maximum parsimony bootstrap support for a clade comprising Amazonetta, Speculanas, Lophonetta, and Tachyeres was 100%, and equally strong support was observed for a clade comprising these four South American genera and Anas. There was no evidence that Amazonetta, Speculanas, Lophonetta, or Tachyeres are closely related to any other waterfowl genera outside Anas.

Both mtDNA and nuclear DNA supported Amazonetta and Speculanas as sister- species, but the relationships of Lophonetta and Tachyeres were less certain.

While Speculanas and Lophonetta are members of the same South American clade, analysis indicates that these partially sympatric species are not sister taxa. The speculum is similar in both species, they both share strong similarities in their displays, as well as tracheal structure (Johnsgard 1978). Molecular data, however, indicate that Speculanas is more closely related to the substantially smaller Amazonetta.

The placement of Tachyeres with these three genera by Johnson and Sorenson (1999) was surprising given the substantial morphological differences among them. Based on genetic data, however, it appears that morphology in steamer ducks is highly derived and divergent from other dabbling ducks. These large-bodied ducks likely evolved sympatrically in Patagonia with Lophonetta and Speculanas, although present day distribution patterns may not reflect their ancestral distribution.

In conclusion, relationships within this distinctive clade of South American ducks were not well resolved despite sequencing more than 10000 characters from six independent linkage groups. This lack of resolution likely resulted from high levels of homoplasy and a lack of informative characters (i.e. soft polytomies), rapid divergence times among genera and species (i.e. hard polytomies), or a combination of these factors. In the case of soft polytomies, it may be possible to resolve relationships by sequencing additional loci and applying phylogenetic methods that incorporate random lineage sorting and mutation (Edwards et al. 2007). In either case, it is clear that this group underwent at least two periods of rapid diversification, one producing the four genera and a more recent radiation among species of Tachyeres. This clade provides a striking example of closely related taxa that have radiated into morphologically and behaviorally divergent forms.

Recommended Citation

Bulgarella, M. (2014). Crested Duck (Lophonetta specularioides), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.creduc1.01