Originally Posted by
Koler-Matznick
According to Wayne, Van Valkenburgh and O'Brien (1991), Nei's genetic
distance between dog and wolf, based on one-dimensional allozyme electrophoresis, is
0.042. This is slightly greater than the 0.030 reported for leopard (Panthera pardus) and
jaguar (Panthera onca). Nei's genetic distances among bear species from single-copy
DNA hybridization are slightly lower than the dog and wolf's (Wayne,Van Valkenburgh
& O'Brien 1991), yet they have not been declared the same species because of the
relatively small genetic/molecular distance.
The available mtDNA evidence is interpreted as indicating that the dog and wolf
could have separated about 76,000 to 135,000 YBP (Tsuda et al.1997; Vilà et al. 1997).
Vilà et al. (1997) found only one mtDNA haplotype shared by wolves and DDs, 25 types
specific to dogs and 26 to wolves. Six of the unique dog types inter-grade with wolf
types on relatedness diagrams (Vilà, et al. 1997). Tsuda et al. (1997) also found that dog
haplotypes, while different, inter-graded with wolves in a neighbor-joining analysis.
From this statistically close relationship of mtDNA types, both Vilà et al. (1997) and
Tsuda et al. (1997) conclude that the wolf is the DD's ancestor. However, in Vilà et al.
(1997) 19 dog types (including primitive dogs') grouped together separately from wolves,
indicating they are monophyletic. The maximum within-dog divergence given is 12
substitutions, the divergence between wolves/dogs as 12 substitutions and between dogs9
and coyote/jackal as 20 substitutions and two insertions. Thus, in mtDNA, dogs are more
distantly related to jackals/coyotes than to wolves. The mtDNA of C. l. pallipes and C. l.
arabs, the wolves closest to primitive dog size and morphology so often proposed as the
DD ancestor (e.g., Gollan 1982; Corbett 1995), are no closer to DD types than other C.
lupus (Vilà et al. 1997). No study found compared dog mtDNA to Canis simensis or
Cuon alpinus.
The mtDNA studies cited above conclude that the DD is a wolf without
addressing the inherent limitations and assumptions of such studies. MtDNA is
essentially a single locus marker, inherited in a clonal fashion, and is only effective at
estimating maternal lineage relationships. The inclusion of nuclear DNA in analyses
would be more meaningful and might lend clarity to the heterogeneity observed in the
mtDNA phylogenetic trees. Cronin (1993: 343) shows that a relatedness tree based on
mtDNA sequence divergence may not be the same as a phylogenetic tree, because
recently differentiated groups will often share a considerable amount of incompletely
sorted genetic characteristics. Incomplete lineage sorting is common among closely
related species with a recent common ancestor. Wayne and Ostrander (1999) emphasize
that, while molecular genetic data seem to support the origin of dogs from wolves, dogs
may have descended from a now extinct species of canid whose closest living relative
was the wolf.
Due to descent from a common ancestor, several species have populations with
mtDNA closer in sequence to another species than to conspecific populations (Carr et al.
1986; Cronin, Vyse & Cameron 1988; Avise, Ankey & Nelson 1990; Cronin et al. 1991).
There are also examples of introgressions of mtDNA between species, which could be
misinterpreted as evidence of conspecific status if analyzed without regard to other
diagnostic characteristics (Avise 1986; Cronin 1993).
Wolves and DDs have been sympatric for thousands to tens of thousands of years,
yet only one mtDNA type is shared. Although occasional hybridization may have taken
place in some areas, panmixia has not occurred despite the fact that until the last few
hundred years most dogs free-ranged, breeding at will (Clutton-Brock 1981; Boitani
1983; Boitani et al. 1995; Nowak 1995; Randi & Lucchini 2002). For example, Indian
pariah dogs are about the same size as the Indian wolf (C. l. pallipes), one of the
candidates for the dog's "ancestral wolf" (Olsen 1985; Hemmer 1990; Corbett 1995),
their estrus seasons coincide, the wolf population today is small and fragmented, yet they
are not known to hybridize (Oppenheimer & Oppenheimer 1975; Shahi 1983; Pal, Gosh
& Roy 1998). If dogs and- wolves did not have relatively effective behavioral barriers to
interbreeding, they would share most if not all of their mtDNA types. Therefore, the dog
and wolf seem to meet the criteria of the Biological Species Concept (O'Brien and Mayr
1991).
The shared or very similar mtDNA types are not necessarily of wolf origin.
Crockford (2000) hypothesizes that the similarity of dog/wolf mtDNA could be due to
genetic introgression of dog into the wolf population. Koop et al. (2000) found some precontact Northwest American aboriginal dogs had mtDNA types closer to North American
wolves than to other DDs, concluding that these DDs may have originated from local
wolves. Crockford (2000) instead hypothesizes that perhaps these mtDNA haplotypes are
similar due to essentially rare unidirectional feral female dog to male wolf hybridization
occurring for so long that extant wolf populations have dog mtDNA.10
Contemporary wild wolf/dog hybrids have been collected in Alaska (B. Yates,
personal communication 2001), Vancouver Island, B.C., Canada (Koop et al. 2000), Italy
(Randi & Lucchini 2002) and are known from the archaeological record (Walker &
Frison 1982). Vilà and Wayne (1999) suggest that, because of reproductive timing
differences, the direction of wolf/dog hybridization was probably female wolves to male
dogs (implying the shared mtDNA types are wolf). They overlook reports that show
male wolves do breed with female dogs (Gottelli et al. 1994) and coyotes (Wayne et al.
1991), and the offspring incorporated into the wolf population. Given the unpredictable
behavior of wolf hybrids and the difficulty of keeping F1 hybrids confined (Gloyd 1992;
Hope 1994; Marx 1994; Steinhart 1995) it is unlikely that prehistorically and in the recent
past, hybrids would have successfully integrated into the DD population. Crockford
(2000) points out that the genetic integrity of specimens used to represent wolves in most
DNA studies are not clearly defined, and concludes that the use of contemporary wolves,
or those from archaeological contexts, in comparative studies of mtDNA with DDs may
be misleading due to the possibility of long-standing introgressive hybridization with
dogs.
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