Systematics

Although phenotypic variation is pronounced, chromatic differences are much subtler. There are only three basic color morphs, constituting a continuous cline (gradient) from light and dark brown, to rufous and grayish brown, proceeding, respectively, east and south along the West Indian Archipelago (see Arendt 2006a: Chapter 3, pages 55-56):

(1) Margarops fuscatus fuscatus (light brown), described as Turdus fuscatus Vieillot 1808; type locality "les grandes îles Antilles et particulièrement à Porto-Ricco et à Saint-Domingue"

Inhabits islands in the Bahamas (or the Lucayan archipelago, which includes the Turks and Caicos Islands), Puerto Rico and small islets and cays in the Greater Antilles (but absent from Cuba, extirpated from Jamaica, and resident only on Beata Island [allied to the Dominican Republic—Hispaniola]), east to Antigua and Barbuda in the northern Lesser Antilles;

(2) M. f. densirostris (dark brown), described as Turdus densirostris Vieillot 1818; type locality not specified in description, restricted to Martinique

Occurs from Montserrat and Guadeloupe south to Martinique (formerly south to St. Vincent and Barbados);

(3) M. f. klinikowskii (rufous), described as Margarops fuscatus klinikowskii Garrido and Remsen 1996; type locality De Barra, Dauphin Qtr., St. Lucia

Restricted to St. Lucia. This subspecies is named for R. F. Klinikowski, "in recognition of his major contributions to ornithology of the Caribbean".

(4) M. f. bonariensis (grayish brown), described as Margarops fuscatus bonairensis Phelps and Phelps; type locality Fontein, Bonaire

Occurs on Bonaire and, formerly, La Horquilla, Los Hermanos Islands, Venezuela

Historically, as with mimids in general, confusion as to the true affinities of the pearly-eye, i.e., whether it was a thrasher or a thrush, was evident early in its classification. Vieillot (1807; corrected date 1808, Browning and Monroe 1991, but their dating called into question by Dickinson et al. 2011) described the species in the genus Turdus, naming it the Pearly-eyed Thrush (Turdus fuscatus). Thereafter, early taxonomists continued assigning the pearly-eye to various genera: Colluricincla, Mimus, Cichlherminia, and Cichlalopia. It wasn’t until 1859 that Sclater described the genus Margarops for this species. Cassin (1861) placed the species in the genus Merula, but in Hartert (1893) and Sharpe (1903) advocated restoring the its placement in Margarops.

The contemporary genus Margarops (Sclater 1859) is derived from the Greek μáργaρos et wψ, translated as "margaros" (S. L. Olson 2005, in litt.) or "pearl" and "ops" (eye) in English (Jobling 1991). The genus presently is known only from the greater Caribbean basin and comprises a single species, Pearly-eyed thrasher (Margarops fuscatus) ("fuscata", Latin for dark, or "fuscare", to darken) (Arendt 2006a: Chapter 3, page 53).

In relation to other Caribbean mimids, phylogenetic analyses of DNA sequence data (from both mitochondrial and nuclear genes) suggest that Margarops is sister to the two species of Cinclocerthia (Brown Trembler C. ruficauda and Gray Trembler C. gutturalis) (Hunt et al. 2001, Barber et al. 2004, Lovette et al. 2012).

Subspecies

Currently one species and four subspecies are recognized in Margarops. Historically, however, two species of Pearly-eyed Thrasher were recognized by taxonomists, a paler species inhabiting the Caribbean's northern (drier) islands (Margarops fuscatus) (Sclater 1859), and a darker species inhabiting the southern (more humid) islands (Margarops densirostris) (Sclater 1859). More recently, however, from analysis of 3,491 base pairs (bp) of mitochondrial DNA (mtDNA) and roughly 780 bp of the nuclear-encoded myoglobin gene, Hunt et al. (2001) used a subset of mtDNA gene sequences and pcr-RFLP (polymerase chain reaction-Restriction fragment length polymorphism) analysis to evaluate the phylogeographic relationships among continental and Caribbean mimids, including the pearly-eye. Although the pearly-eye shows no close affinities to continental mimids (thrashers, Toxostoma sp.), it displays only a moderate level of ancestral variation. Mitochondrial haplotypes were partitioned into three clades, but these clades lack any apparent geographical pattern. The relative numbers of individuals from Montserrat, Guadeloupe, and Dominica that were assigned to clades B and C, in comparison to clade A, i.e., M. f. fuscatus that predominated on islands to the north, may suggest an extended period of separation between pearly-eye populations in the northern and southern parts of its range. This was corroborated in a comparison of appendicular measurements (see discriminant function analysis graph under Measurements: subspecific meristics).

Additional taxonomic history can be found in Arendt (2006a: Chapter 3).

Hybridization and Swamping

Pearly-eyed Thrasher is among the recently expanded West Indian species in which genetic divergence within a single island population exceeds 0.5% (Hunt et al. 2001). Populations in the northern Lesser Antilles contain three clades of mtDNA having average pairwise genetic distances of 0.7%, 1.0%, and 1.2% (Hunt et al. 2001). Although the clades are only partly spatially segregated, they also present evidence of recent gene flow between formerly divergent island populations (Ricklefs and Bermingham 2007).

In a morphometrics study (Arendt 2006: Chapter 5, figure 5.7, page 129) a discriminant function analysis of five appendicular characters showed more gene flow between the two more northern subspecies (M. f. fuscatus and M. f. densirostris). The classification matrix, as well as a jackknifed classification matrix, showed that 80% of the characters of the southern subspecies (M. f. bonariensis) were classified correctly, whereas the same was true of only 50% of each of the two more northern subspecies.