How Science Works - Giraffes - A single Pan-African Species Or Several Distinct Species?

Giraffe trio crossing plain, Etosha, Namibia

Photo: Mogens Trolle

Reticulated giraffe, Buffalo Springs, Kenya. Photo: Mogens Trolle

Photo: Mogens Trolle

Gene flow in giraffes and what it means for their conservation – Department of Biology - University of Copenhagen

In an evolutionary picture that resembles that of humans, giraffes appear to have speciated, or partially speciates at different times and in different parts of their range, then hybridized, before splitting again with regular gene-flow between the groups.

Similarly, though over a greater range, humans seems to have partially speciated into isolated populations in Africa before coming together again and spreading to Eurasia as Homo erectus which then split into Neanderthals, Denisovans and possibly others before meeting up with H. sapiens coming out of Africa in a second wave, to interbreed with the Eurasian species. The result is genetically distinct populations with evidence of ancient hybridization and gene flow.

Because conservation efforts tend to be directed at the species level, it is important for giraffe conservation to determine whether there is a single pan-African species with local sub-species or whether there are four or more species, each with a smaller population and therefore more vulnerable to habitat destruction and extinction.

To try to resolve this issue, as part of the African Wildlife Genomics research framework led by research groups at the Department of Biology at the University of Copenhagen, scientist carried out an extensive genome analysis to establish whether the different populations have been genetically isolated for long enough to be regarded as distinct species, even though, in captivity, they freely interbreed.

The results were a little surprising but highlight the difficulty in determining whether speciation has occurred within a population where differentiation is still in progress and few barriers to hybridisation have arisen. The problem is compounded by the fact that there is not a fixed definition of species, although biologists understand what the term means in a given context.

I've previously written blog posts about this problem, using the Eurasian crows as an example - an article incidentally which was recommended reading for Scottish biology students doing their 'Highers'.

The researchers have published their findings open access in the online Cell Press journal, Current Biology and explain it in a news item from the University of Copenhagen Biology Department:

Creationism in Crisis - How Killer Whales Were Evolving Cultural Groups - 20,000 Years Before 'Creation Week'

Researchers find 20,000 years old refugium for orcas in the northern Pacific - SDU

The northern Pacific near Japan and Russia is home for several different groups of orcas. They have no contact with each other, do not seek the same food, do not speak the same dialect, and do not mate with each other. Some are the descendants of a pod that moved there during the last Ice Age.

Any study of whales, such as dolphins and they larger cousins, the orca's or killer whales will quickly dispel one of the myths creationists use to try to justify their absurd belief that humans are somehow materially different to the rest of life on Earth in a way which isn't just because we are a variation on the general mammalian theme with enough distance between us and related species to justify a separate taxon, because we were specially created - humans form cultures and have languages and traditions, etc.

Of course, it's not just the whales that have cultures and languages; chimpanzees and bonobos and other primates also have distinct cultural groups that differ significantly from one another, but this article deals specifically with orcas and the research which has shown that they moved into Ice Age refugia at the last glacial maximum, some 20,000 years ago, and some have slayed there ever since.

The article also illustrates a problem of modern taxonomy in how to define a species with hard and fast rules when the distinction in reality is fuzzy. Some of the pods studied form isolated cultural groups that seek different foods to the others, which speak a different dialect, move in a specific area, and never interbreed. This cultural barrier to hybridization is as much a barrier as is the different plumage and mating rituals that are the pre-zygotic barriers to interbreeding that justify classifying many related birds as distinct species because the barriers ensure an isolated gene pool in species that could successfully interbreed and do so in captivity. Killer whales exist in many pods with cultural barriers to interbreeding and so form isolated gene pools, yet they are regarded as a single species.

To overcome this problem, biologists have classified the different killer whale pods into 'ecotype', but it is this genetic isolation that enables genetic analysis to determine how long the pod has been isolated.

A research team led by whale biologist, Olga Filatova, of the University of Southern Denmark recently published an open access paper in the journal Marine Mammal Science showing how environmentally stable marine regions may have preserved refugial populations of the killer whale that retained historical genetic and cultural diversity. These whales are believed to have moved into the warmer refugia during the last Ice Age.

The team's work is explained in a University of Southern Demark (SDU) press release by Birgitte Svennevig:

Creationism in Crisis - Urban Great Tits Have Beome Paler Than Their Rural Relatives

Urban (left) and rural (right) great tits, Parus major

Photo: Caroline Isaksson

European great tit, Parus major.

Source

Urban great tits have paler plumage than their forest-living relatives | Lund University

In an example of how the environment, and in this case probably the availability of different food items, can cause changes on which natural selection can act, a study by an international team or reserchers led by Pablo Salmón of Lund University, Sweden, has shown that great tits, Parus major living in an urban environment have paler breasts than those living in a forest environment.

Although this is probably not an evolutionary change, i.e., a change in the frequency of alleles in the population gene pools, as the cause is probably dietary difference, it illustrates how an environmental change can produce changes in features on which natural selection can act to bring about true evolutionary changes, and so begin the process of allopatric speciation.

Of course, there will be creationists who will misrepresent the scientific fact of evolution, either deliberately, or mendaciously in order to mislead others, who will dismiss this as "not evolution", not for the reason given above but because "they're still great tits/still birds" and haven't grown a new structure or turned into an unrelated taxon.

The research is explained in a Lund University press release: