Subsequent isolation of the Atlantic Ocean from the Pacific Ocean by the Bering Landbridge facilitated allopatric
divergence of the Atlantic lineage, leading to black guillemots.
Positive values are associated with alligator snapping turtles, and negative values are associated with eastern snapping turtles Standardized Canonical Discriminant Function Coefficients Function 1 2 Mud -0.058 -0.001 Water temperature 0.431 -0.027 Aquatic vegetation -0.597 0.682 Physical structure 0.433 0.588 Water depth 0.620 0.469 Detritus 0.318 -0.550 TABLE 5.--Summary of Canonical Discriminant Functions assessing similarity or dissimilarilty between habitat variables at capture locations where eastern snapping turtles (Chelydra serpentina) were found in sympatry with alligator snapping turtles (Macrochelys temminkii) and allopatric
eastern snapping turtles characterized by habitat variables at capture sites.
No significant effect was found for either fixed factor or their interaction (Tables 2 and 3), indicating an absence of strong reproductive barriers for allopatric
Whereas the causes of this discrepancy are unknown, the lower gamete compatibility in sympatric versus allopatric
crosses is nevertheless consistent with reinforcement of reproductive isolation in sympatry (Noor 1999).
The pattern of allopatric
distribution among these four related species is shown by several other Bothriurus species groups, e.g., the prospicuus group (Mattoni & Acosta 1997; Acosta & Peretti 1998; Ojanguren Affilastro 2002; Mattoni 2003), the vittatus group (Mattoni 2002a, 2002b, 2002c), and the patagonicus group (Mattoni & Acosta, unpub.
The two species have a largely allopatric
altitudinal distribution on Hokkaido Island, Japan, proposed to be the result of temperature-mediated competition.
As with any set of allopatric
populations, the question is not trivial.
(2008) found a clear split between haplotypes into two allopatric
groups, one from the Padano-Venetian district and one from the Danubian district, thus supporting the taxonomic arrangement of Kottelat (1997).
Such similarities in allopatric
species are already reported for crickets, with similar songs in different Anaxipha species from Panama and Ecuador, and also from two Phyllopalpus species from Panama and Argentina (Riede 2009).
Both of these species are distantly allopatric
and have restricted distributions, as is also commonly observed in other species in the genus, e.g.
Baboons are not found on Bioko Island or in mainland Equatorial Guinea near Bioko Island and are allopatric
with drills on the mainland.