Reticulata or camelopardali? Something for armchair taxonomists to chew over. Photo: Wikimedia Commons
Reticulata or camelopardali? Something for armchair taxonomists to chew over. Photo: Wikimedia Commons

Earth is home to an estimated 1 trillion species, of which only about 1.2 million have been described scientifically. There’s good reason to increase this number: each species could offer an adaptive, evolutionary solution to the many challenges presented by changing landscapes.

Biological species are often comprised of geographically distinct entities. These are known as subspecies, races or management units.

Taxonomists and phylogeographers armed with this information ought to be able to identify those species with multiple evolutionary “solutions” in progress. These “solutions” should then be catered for to ensure the relevant species can be effectively conserved.

But this approach hasn’t been particularly successful, as the story of one giraffe species shows.

Giraffa camelopardalis has traditionally been partitioned into 11 subspecies. New research suggests it actually comprises only four morpho-genetic “entities” within it that warrant conservation action.

All four should be elevated to full species status. Why? To greatly simplify the strategy that’s needed for effective giraffe conservation.

A similar approach could help in developing meaningful conservation plans for many other species.

A new approach is needed

The subspecies category has been blatantly and subjectively misused to name biologically trivial entities. Historically, it was heinously abused to recognise up to 30 “races” of humans.

It’s difficult to sort out the conservation “wheat” from the “chaff” when too many subspecies are defined. It diverts conservationists’ attention from what’s really important to maintain current diversity. It also distracts them from what is needed to cater for species’ ongoing evolution.

It’s time to rethink which entities are worthy “currency” for comparative biological research and conservation action. The answer might lie in evolutionarily significant units, or ESUs.

Taxonomists could then identify structured morphological and genetic variation within species. They could also highlight species’ evolutionary capacities to respond to changing environments. The greater this capacity, the more species can contribute to long-term macro-biodiversity over the landscape they occupy.

We tested this approach on two species: the helmeted guinea fowl, and the pocket gopher.

The fowl…
… and our closer cousin

Conservation strategies

There are currently 31 recognized subspecies of helmeted guinea fowl. The evolutionarily significant units approach reduced this number to nine. For the pocket gopher, the number dropped from 195 to three.

There are three important points of assessment in this approach.

First is the co-possession of multiple, correlated morphological characteristics and genetic markers. These suggest a common phylogeographic genealogy.

Second is the co-possession of heritable, arguably adaptive anatomical, behavioural and ecological differences. These suggest there has been constrained interbreeding between well-marked subspecies.

Third is having geographically similar distributions to those of other well-marked evolutionarily significant units and full species.

This approach has enormous potential. If it’s properly applied, it could maximize the biggest evolutionary “bang” for limited conservation “bucks.” It’s a positive step towards focusing conservation efforts on products of past and ongoing evolution.

Conservation strategies should be directed towards maintaining the process of evolution, not just preserving its perceived products. Scientists need to understand more about how evolution in particular species has occurred. Then they can plan for those species’ future survival.

Tim Crowe, Emeritus Professor, University of Cape Town and Paulette Bloomer, Professor of Genetics, University of Pretoria

This article was originally published on The Conversation. Read the original article.