Evolutionaire verscheidenheid en verspreiding van papegaaien over de continenten

Thursday, February 23, 2012

Evolutionary diversification and biogeography of parrots

by John Terbot

Gondwana, the ancient supercontinent consisting of most current landmasses in the Southern hemisphere, is the geographic origin of parrots. This is a diverse order of birds comprised of 3 families, 88 genera, and 386 species (http://www.zoonomen.net/avtax/psit.html). They are currently present on most Southern-hemisphere landmasses (aside from Antarctica) and in tropical regions worldwide. However, they are notably species-rich in Australia and Indo-Malaysia. The contemporary distribution of parrots illustrates the importance of a multi-faceted approach to explain speciation. The use of vicariance (speciation through geographic isolation notably through continental drift and mountain uprising), dispersal (the transfer of an organism across a distance to found a new population in a novel area), and adaptive radiation (through the adaptive use of a new resource) are now accepted as equally necessary to explain the observed diversity of life.

To appreciate the speciation of parrots, and other Gondwandan organisms (those originating in the Southern hemisphere), an understanding of the separation of Gondwana due to plate tectonics is needed. For brevity, modern names for landmasses will be used, however it is important to remember that over geological time the coastlines and amount of emergent land varies. Gondwana (South America, Africa, Australia, New Zealand, Madagascar, India, Antarctica) and Laurasia (North America, Europe, Asia, Greenland) formed a continuous landmass from 220 Ma to 160 Ma when Laurasia began drifting North. Over the course of the next 22 million years (160 to 138 Ma), Africa separated from Antarctica (Upchurch et al. 2002). During this time, Africa remained attached to South America until 100 to 105 Ma, was relatively isolated until 40 Ma, and began to collide with Eurasia around 30 Ma (Hedges 2001). Around this time, 45 to 90 Ma, Australia started to separate from Antarctica but remained relatively close until 45 Ma (Cox 2000).

The first lineage of parrots to diverge was Strigopidae, a family found only in New Zealand and on Norfolk Island. While it was traditionally thought to have occurred during the split of New Zealand from Antarctica around 80 Ma, phylogenetic analysis reveals that this split happened around 58.6 Ma, long after New Zealand became geographically isolated (Schweizer et al. 2011). However, there is some evidence that New Zealand may have been completely submerged during the Oligocene (34 to 23 Ma; Waters and Craw 2006), indicating that these endemic parrots may have colonized New Zealand after their divergence.

The Australian split from Antarctica around 40 Ma corresponds with a major divergence in parrots between mostly Australasian and Indo-Malaysian taxa and those from neotropical and afrotropical regions. The neotropical, Arini, and afrotropical, Psittacini, lineages separated from each other around the Eocene-Oligocene boundary, indicating a relation to the rapid cooling of this time (Cox 2000) and a potential origin from an Antarctic population that was pushed North by expanding ice sheets (Schweizer et al. 2011).

Other parrots found on the African continent, genus Agrapornis, likely represent further dispersal from Madagascar. Madagascar was likely populated itself from two separate dispersal events. The first from an Australasian origin giving rise to members of Coracopsis around 28 Ma and a second giving rise to the Agrapornis taxa from an Australasian or Indo-Malasay origin around 24 Ma.

These Westward dispersal events of parrots occurred around the time that the modern geographic placement of Australasia and Indo-Malaysia formed. Therefore, in addition to the clear single-direction dispersals, dispersal events among the abundant island formations of the Australasia and Indo-Malaysia regions led to multiple speciation and divergence events between both regions during the Neogene (Schweizer et al. 2011).

Along with this rapid divergence and dispersal of parrots, an ecological divergence also occurred that would lead to the group known as lories. As demonstrated by their brush-tipped tongues, a dietary shift occurred leading to a use of nectar as a food source. This novel food source has led to an extremely rapid speciation (approximately 53 species) considering their divergence from other parrots occurred as recently as the middle Miocene (Schweizer et al. 2011).

This comprehensive explanation of the distribution and divergence of parrots serves to illustrate two large trends in macro-evolutionary studies. The first is that when viewed with other bird taxa, it becomes clear that birds were co-existent with dinosaurs and diverged into major taxa (e.g., parrots) prior to the late Cretaceous even that led to the extinction of dinosaurs. As well, it illustrates well the importance of multiple theories to explain the diversity of species. Vicariance, climate change induced dispersal, trans-oceanic dispersal, and ecological changes must all be used to accurately describe and explain the observed molecular phylogenies.


References Cited:

Cox CB (2000) Plate tectonics, seaways and climate in the historical biogeography of mammals. Memórias do Instituto Oswaldo Cruz, 95, 509–516.

Hedges SB (2001) Afrotheria: Plate tectonics meets genomics. Proceedings of the National Academy of Sciences of the United States of America, 98, 1-2.

Schweizer M, Seehausen O, Hertwig ST (2011) Macroevolutionary patterns in the diversification of parrots: effects of climate change, geological events and key innovations. Journal of Biogeography, 38, 2176-2194.

Upchurch P, Hunn CA, Norman DB (2002) An analysis of dinosaurian biogeography: evidence for the existence of vicariance and dispersal patterns caused by geological events. Proceedings of the Royal Society B: Biological Sciences, 269, 613-621.

Waters JM, Craw D (2006). Goodbye Gondwana? New Zealand Biogeography, Geology, and the Problem of Circularity. Systematic Biology, 55, 351-356.

http://www.zoonomen.net/avtax/psit.html

http://commons.wikimedia.org/wiki/File:Kea_%28Nestor_notabilis%29_-on_ground-8.jpg

http://commons.wikimedia.org/wiki/File:LoryTongueLyd4.png

Posted by Andi Wolfe at 7:50 AM

Labels: birds, Gondwana, Parrots

Publications of Stefan T Hertwig

·         The evolutionary diversification of parrots supports a taxon pulse model with multiple trans-oceanic dispersal events and local radiations.

Authors: Manuel Schweizer, Marcel Güntert, Ole Seehausen, Stefan T Hertwig

Molecular phylogenetics and evolution. 09/2009;

Vicariance is thought to have played a major role in the evolution of modern parrots. However, as the relationships especially of the African taxa remained mostly unresolved, it has been difficult to... [more]Vicariance is thought to have played a major role in the evolution of modern parrots. However, as the relationships especially of the African taxa remained mostly unresolved, it has been difficult to draw firm conclusions about the roles of dispersal and vicariance. Our analyses using the broadest taxon sampling of old world parrots ever based on 3219 bp of three nuclear genes revealed well-resolved and congruent phylogenetic hypotheses. Agapornis of Africa and Madagascar was found to be the sister group to Loriculus of Australasia and Indo-Malayasia and together they clustered with the Australasian Loriinae, Cyclopsittacini and Melopsittacus. Poicephalus and Psittacus from mainland Africa formed the sister group of the Neotropical Arini and Coracopsis from Madagascar and adjacent islands may be the closest relative of Psittrichas from New Guinea. These biogeographic relationships are best explained by independent colonization of the African continent via trans-oceanic dispersal from Australasia and Antarctica in the Paleogene following what may have been vicariance events in the late Cretaceous and/or early Paleogene. Our data support a taxon pulse model for the diversification of parrots whereby trans-oceanic dispersal played a more important role than previously thought and was the prerequisite for range expansion into new continents.