- Email: [email protected]
Flying kiwis and pattern information in biogeographic hypotheses
CORRESPONDENCE
[4,5] for example) South America and ‘New Zealand 1’ are still supported as the most likely ancestral areas (Table 1). The conjunction of such ad hoc New Zealand sub-areas could imply separate biogeographic histories for moa and kiwi endeism without any assumptionof dispersal. References 1.
COOPER A, MOURER-CHAIJVIRE C, CHA~%~ERSGK, VON HAESLER A, S: Independent origins of New Zealand WLSON AC, PAAE%O
2.
Moas and kiwis. Proc Mat1 Acud Sci USA 192, 89~8741-8744. MAY RM: Which were the real New Zealanders? Curr Biol
3.
BREMER K: Ancestral areas a cladistic
4.
5.
1993,3:3637. reinterpretation of the center of origin concept. Systematic Biol 1992, 41:436445. CRAW R: Continuing synthesis between panbiogeography, phylogenetic systematics and geology as illustrated by empirical studies on the biogeography of New Zealand and the Chatham Islands. System&c Zool 1988, 37:291-310. HUMPHFSES CJ, PARENTI L: CLad&tic Biogeog??apby. Oxford: Clarendon
Press; 1986.
Victor A Albert and K%e Bremer, Department of Systematic Botany, Uppsala University, Villavggen 6, S75236 Uppsala, Sweden.
Robert M. May replies: Many questions about the evolutionary relationships among groups of organisms, and about their past geographic distributions, will forever be beset with ambiguities and uncertainties. Even though new windows into the past continue to open - through advances in molecular biology and elsewhere, and through new approaches to analysing the resulting data - we still see through a glass, darkly. In those circumstances, when new and different lines of approach to a specific phiylogenetic or biogeographical question tend to agree with older answers, confidence grows. But when new apiproaches give answers at odds with earlier work, I believe we should keep an open mind, using commonsense and judgement to weigh one alternative line of evidence against another. Here I part company with many cladists, some of whom believe their particular methodology is the One True Way, by virtue of its supposed objectitity. Which brings us to Albert and Bremer, and the past biogeography of the ratites. My recent review [2] dealt with Cooper et al’s [l] sign&ant reinterpretation of the phylogeny of these birds, based on new molecular
studies. I followed Cooper et al. in concluding that given the new phylogenetic tree, and given the positions of the relevant continents and islands over the time period in question - the New Zealanders’ emblematic kiwi may be a relatively recent arrival from Australia. As an Australian, I enjoy the possible irony. To the contrary, Albert and Bremer use Bremer’s [3] new approach to ‘centres of origin’ to conclude essentially that kiwis and moss are more likely to have grown up together in New Zealand, and subsequently.spun off emus and cassowaries to Australia, and ostriches to Africa. Bremer’s [3] new approach to these kinds of questions is interesting, but has some off features (which shares with much else in cladistics). Cladistic analyses-are based on lirst identifying a list of ‘character states’ pertaining to the organisms under study, and then using parismony or some equivalent criterion to construct the most probable pattern of relationships among the organisms. There can, however, be problems in deciding exactly how to build the list of ‘character states’; this enterprise is often much less objective than is apparent. In Bremer’s [3] cladistic approach to biogeographical questions, ‘each is treated as a single character, which may be optimised onto the cladogram using either forward or reverse Camin-Sokal parsimony’. That is, no account is taken of the relative sizes of land masses, nor of where they sit today and sat in the past on the surface of the globe, divided by oceans of varying sizes. Those not familiar with the enthusiastic excesses of some cladistic analyses may iind this surprising, not to say silly. It is biogeography without the geography. In short, I welcome Albert and Bremer’s comments which provide a different perspective, forcing us to think agtin about the biogeographical conclusions drawn by Cooper et al. [l] from their molecular phylogeny of the ratites. But I believe any such biogeographical studies must, at some level, deal with the actual geography of land masses and seas; regions cannot sensibly be treated as ‘characters’ in a geography-free matrix. And so I am not convinced by Albert and Bremer’s conclusions about the ratites.
Robert M. May, Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
325
[4,5] for example) South America and ‘New Zealand 1’ are still supported as the most likely ancestral areas (Table 1). The conjunction of such ad hoc New Zealand sub-areas could imply separate biogeographic histories for moa and kiwi endeism without any assumptionof dispersal. References 1.
COOPER A, MOURER-CHAIJVIRE C, CHA~%~ERSGK, VON HAESLER A, S: Independent origins of New Zealand WLSON AC, PAAE%O
2.
Moas and kiwis. Proc Mat1 Acud Sci USA 192, 89~8741-8744. MAY RM: Which were the real New Zealanders? Curr Biol
3.
BREMER K: Ancestral areas a cladistic
4.
5.
1993,3:3637. reinterpretation of the center of origin concept. Systematic Biol 1992, 41:436445. CRAW R: Continuing synthesis between panbiogeography, phylogenetic systematics and geology as illustrated by empirical studies on the biogeography of New Zealand and the Chatham Islands. System&c Zool 1988, 37:291-310. HUMPHFSES CJ, PARENTI L: CLad&tic Biogeog??apby. Oxford: Clarendon
Press; 1986.
Victor A Albert and K%e Bremer, Department of Systematic Botany, Uppsala University, Villavggen 6, S75236 Uppsala, Sweden.
Robert M. May replies: Many questions about the evolutionary relationships among groups of organisms, and about their past geographic distributions, will forever be beset with ambiguities and uncertainties. Even though new windows into the past continue to open - through advances in molecular biology and elsewhere, and through new approaches to analysing the resulting data - we still see through a glass, darkly. In those circumstances, when new and different lines of approach to a specific phiylogenetic or biogeographical question tend to agree with older answers, confidence grows. But when new apiproaches give answers at odds with earlier work, I believe we should keep an open mind, using commonsense and judgement to weigh one alternative line of evidence against another. Here I part company with many cladists, some of whom believe their particular methodology is the One True Way, by virtue of its supposed objectitity. Which brings us to Albert and Bremer, and the past biogeography of the ratites. My recent review [2] dealt with Cooper et al’s [l] sign&ant reinterpretation of the phylogeny of these birds, based on new molecular
studies. I followed Cooper et al. in concluding that given the new phylogenetic tree, and given the positions of the relevant continents and islands over the time period in question - the New Zealanders’ emblematic kiwi may be a relatively recent arrival from Australia. As an Australian, I enjoy the possible irony. To the contrary, Albert and Bremer use Bremer’s [3] new approach to ‘centres of origin’ to conclude essentially that kiwis and moss are more likely to have grown up together in New Zealand, and subsequently.spun off emus and cassowaries to Australia, and ostriches to Africa. Bremer’s [3] new approach to these kinds of questions is interesting, but has some off features (which shares with much else in cladistics). Cladistic analyses-are based on lirst identifying a list of ‘character states’ pertaining to the organisms under study, and then using parismony or some equivalent criterion to construct the most probable pattern of relationships among the organisms. There can, however, be problems in deciding exactly how to build the list of ‘character states’; this enterprise is often much less objective than is apparent. In Bremer’s [3] cladistic approach to biogeographical questions, ‘each is treated as a single character, which may be optimised onto the cladogram using either forward or reverse Camin-Sokal parsimony’. That is, no account is taken of the relative sizes of land masses, nor of where they sit today and sat in the past on the surface of the globe, divided by oceans of varying sizes. Those not familiar with the enthusiastic excesses of some cladistic analyses may iind this surprising, not to say silly. It is biogeography without the geography. In short, I welcome Albert and Bremer’s comments which provide a different perspective, forcing us to think agtin about the biogeographical conclusions drawn by Cooper et al. [l] from their molecular phylogeny of the ratites. But I believe any such biogeographical studies must, at some level, deal with the actual geography of land masses and seas; regions cannot sensibly be treated as ‘characters’ in a geography-free matrix. And so I am not convinced by Albert and Bremer’s conclusions about the ratites.
Robert M. May, Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
325