Convergence of Genetic and Morphological studies on atlantis

Convergence of Genetic and Morphological studies on atlantis

References

1) de Knijff, P, Denkers, F, van Swelm, N D, and Kuiper, M, Genetic affinities within the Herring Gull Larus argentatus assemblage revealed by AFLP Genotyping, J Mol Evol 52 85-93 (2001).

2) Collinson, M, Genetic relationships among the different races of Herring Gull, Yellow-legged Gull and Lesser Black-backed Gull, British Birds 94(11) 523-528 (2001). [2] is interpretation and summary of [1]

3) Liebers, D, Helbig, A J, and de Knijff, P, Genetic differentiation and phylogeography of gulls in the Larus cachinnans-fuscus group (Aves: Charadriiformes), Molecular Ecology 10 2447-2462 (2001).

4) Rossiter, N, Characteristics of Atlantic Yellow-legged Gulls (October 2001).

5) Rossiter, N, Intersection Atlantic-Mediterranean Yellow-legged Gulls in Gibraltar/ Andalucia (Spain)/ Tanger (Morocco) area (April 2002).

6) Rossiter, N, Mediterranean Yellow-legged Gulls in south-west Spain (March 2002).

7) Rossiter, N, (2002), Yellow-legged Gulls in the Atlantic-Mediterranean Intersection Zone, 6th International Gull Meeting, August 2002, Lammi, Finland.

Notes from references:

In [1,2] it is claimed that there is very little differentiation between atlantis and michahellis. The populations studied were:

Site


Country	Sample size	Claimed form
Berlengas	Portugal	5	atlantis
Essaouira	Morocco	5	atlantis
Gibraltar		6	michahellis

There was slightly more affinity between argenteus and atlantis than between graellsii and atlantis. The form cachinnans was thought to be ancestral to all the other taxa studied.

In [3] summary from atlantis perspective:

Subspecies studied of Yellow-legged Gulls:

atlantis (eastern North Atlantic Ocean)

michahellis (Mediterranean Sea)

armenicus (inland lakes of Anatolia, Armenia, Iran)

cachinnans (Black, Caspian, Aral Seas)

barabensis (western Siberia)

mongolicus (central Asian steppe region)

Technique: the most variable part of the mitochondria (HVR-I) was used.

Some of the populations studied:

Claimed form


Group code	Colony/country	Sample size
atlantis	atlAZO	Azores	20
	atlMDR	Madeira	20
	atlMDR	Morocco	7
	atlBER	W Portugal	17
	atlGAL	Galicia [not actually NE Spain]	30
michahellis	micWeM	Gibraltar	11
	micWeM	Camargue	18
	micWeM	Alsac	12
	micWeM	NW Italy	7
	micEaM	Malta	15
	micEaM	Crete	9
	micEaM	Constanta	6

Restriction of gene flow: graellsii/ atlantis-michahellis:

Two graellsii haplotypes were detected in atlantis (Morocco/Portugal) indicating that introgression occurs at a very low level.

Degree of Differentiation between Populations [note in table 3: a few column headings appear to need slight adjustment]:

The form michahellis has a more shallow haplotype and lower nucleotide diversity than atlantis and its haplotypes are a subset of atlantis, suggesting that michahellis is derived from atlantis as the older lineage.

The form cachinnans plays a similar role in the lineage of eastern forms.

The forms cachinnans and atlantis both have held large populations over long periods. Both today reside in areas of relative climatic stability. In the eastern North Atlantic Ocean, some north-south range shifts may have occurred during ice ages but no major population bottlenecks or range restrictions have occurred.

The michahellis population is less diverse than atlantis with no significant geographical variation while there is significant differentiation within all five atlantis colonies analysed.

An unexpected differentiation was found between northern atlantis (Azores, west Portugal and Galicia) and southern atlantis (Madeira, Morocco). Since northern atlantis is similar to michahellis in many respects, this suggests that the southern atlantis contributed little to michahellis.

The forms atlantis and graellsii belong to different major clades and are not each other's closest relatives, as surmised initially by Dwight in 1922.

Gene flow between atlantis and michahellis is probably continuing because of the connection of the Atlantic to the Mediterranean at Gibraltar. Also michahellis is breeding now on the Atlantic coast of France further increasing he likelihood of genetic exchange with atlantis.

The time of the population-level separation between atlantis and cachinnans is estimated at 256,000-295,000 years, perhaps due to a glacial maximum around this time.

Comments (Nick Rossiter):

Further study of the genetics is needed to confirm whether [1] or [3] gives a more accurate picture.

The sample sizes in [1] are small and it is highly debatable whether Gibraltar is a sound choice as the source for michahellis. The Yellow-legged Gulls here are intermediate between atlantis and michahellis morphologically and appearance can vary considerably from port to port over a short distance [5].

In [3] the experimental design is improved: Gibraltar is still used as a source of michahellis but the sample from here is diluted with a number of other sources included as well.

The forms atlantis and michahellis are differentiated in [3], particularly the Southern atlantis and michahellis forms.

No differentiation was found between western and eastern michahellis in the Mediterranean.

The differentiation in [3] between Southern atlantis and northern (Iberian) atlantis gives independent corroboration of the forms emerging from the morphological studies of [4].

The significant differentiation in [3] between one atlantis population and another gives independent corroboration of the variety of forms found in the morphological studies of [4].

The identification of the Atlantic Ocean-Mediterranean Sea intersection as a gene mixing zone is also supported by the morphological studies of [5,7] which found a population with characteristics between atlantis and michahellis in this area.

Although michahellis is also now breeding on the Atlantic in south-west Spain [6], the two forms are occupying a different biotope thus reducing the chance of gene flow between atlantis and michahellis [7].

The results of a recent visit to Madeira (March 2002) indicate that the form here is similar to that in the eastern Canaries (calls and structure) and the western Canaries (wingtip pattern) so the Madeira form is a typical southern atlantis.

The results for the Azores of [3] appear surprising since all previous authors have indicated that morphologically the gulls here are closer to those in the Canaries and Madeira than to those of the Mediterranean. Indeed some authors including Dubois (2001) think that the Azores form is relatively distinctive among the various Atlantic forms. However, there is a shortage of comparative studies with large sample sizes and a visit to the Azores to attempt this task is anticipated.

There is no treatment in [3] of the Cantabrican Atlantic Yellow-legged Gull and the argenteus of south-west France. This is a perspective that needs to be tackled for determining whether Iberian atlantis is a cline between argenteus and southern atlantis, as one suggestion in [4]

Conclusion:

In the eastern North Atlantic Ocean, the morphological studies [4] and genetic studies [3] are converging. But work is still incomplete. More morphological studies are required on the Azores population. More DNA studies would also be welcome to see if consensus emerges.

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