animal systematics lecture 4
TRANSCRIPT
INFRASPECIFIC CATEGORIES (continued)
THE MALE OFFSPRING OF SUBSPECIES ARE OFTEN STERILE
RACE: local populations with in subspecies. • not recognized in the taxonomic
hierarchy. • Subspecies and geographical race are
used synonymously by taxonomist of mammals, Birds and Insects. • Since No two localities have identical
environment, every subspecies is at least theoretically also an ecological race.
RACE • Imp. Taxonomically are host races
among parasites and species-specific plant feeders. • If gene flow between populations on
different hosts is drastically reduced such host races are the equivalent of geographic races in free living animals. • such host races often develop subspecific
characters.
The Question: whether geographic separation is essential for speciation? or whether sympatric speciation occurs?
___ Rhagoletis pomonella( apple maggot fly)
diverged into 2 host races 1. apple 2. hawthorne__ Sympatric, BUT different fruiting
times of the two hosts.
• Hawthorn
• Apple:
• Hawthorn Berry . Apple
• Lake Malawi Lake Victoria
relatively young. 1 million year old
100s of Species
• Yong-Jin take a close look at a group of rock-dwelling species from Lake Malawi. To gain resolution, they used a new type of genetic marker that includes a microsatellite and linked sequence.• some of these species have formed
within the past few thousands years and that gene exchange is ongoing between species at some loci
cline(Gr. Gradient)
Julian Huxley in 1938. • An ecocline or cline consist of ecotypes
or forms of species that exhibit gradual phenotypic and/or genetic differences over a geographical area, typically as a result of environmental heterogeneity.
cline• Genetically, clines result from
the change of allele frequencies within the gene pool of the group of taxa in question. • Clines may manifest in time
and/or space.
cline•Clines – Gradient in features within a species over space or time• Cline is a character Gradient, not a
category. A single population may belong to as many different clines as it has characters.
cline• A cline is formed by a series of
contiguous populations in which a given character changes gradually. • Any genetically determined
character, may vary clinally. Clines may be smooth, or they may be step clines with rather sudden changes of values.
• Example of Cline in Salamander Ensatina escholtzii
• C
GAP IN RING
• Clines do not receive nomenclatural recognition.
• When the geographic variation of a species is clinal, it is usually inadvisable to recognize subspecies, except possibly for the two opposite ends of the cline when they are very different .
Ring species – Cline over space (biogeographic) that results in failure of end members to interbreed, e.g. In Sea gulls.
• Ring species are a distinct type of cline where the geographical distribution in question is circular in shape, so that the two ends of the cline overlap with one another, giving two adjacent populations that rarely interbreed due to the cumulative effect of the many changes in phenotype along the cline.
• The populations elsewhere along the cline interbreed with their geographically adjacent populations as in a standard cline.
• Ring species present an interesting problem for those who seek to divide the living world into discrete species, as chain species are closely related to speciation (in this case, parapatric).
• Ring species are a distinct type of cline where the geographical distribution is circular in shape, so that the two ends there are two adjacent populations that rarely interbreed
• The populations elsewhere along the cline interbreed
• Ring species present an interesting problem for those who seek to divide the living world into discrete species, as chain species are closely related to speciation (in this case, parapatric).
• A classic example of ring species is the Larus gulls circumpolar species "ring". North Pole.
• The Herring Gull L. argentatus, which lives primarily in Great Britain and Ireland, can hybridize with the American Herring Gull L. smithsonianus, (living in North America), which can also hybridize with the Vega or East Siberian Herring Gull L. vegae, the western subspecies of which, Birula's Gull L. vegae birulai, can hybridize with Heuglin's gull L. heuglini, which in turn can hybridize with the Siberian Lesser Black-backed Gull L. fuscus. All four of these live across the north of Siberia. The last is the eastern representative of the Lesser Black-backed Gulls back in north-western Europe, including Great Britain.
A Herring Gull, Larus argentatus (front) and a Lesser Black-backed Gull. Larus fuscus (behind) in Norway: two species with clear differences.
• The Lesser Black-backed Gulls and Herring Gulls are sufficiently different that they do not normally hybridize; thus the group of gulls forms a continuum except where the two lineages meet in Europe.
• all that distinguishes a ring species from two separate species is the existence of the connecting populations - if enough of the connecting populations within the ring perish to sever the breeding connection, the ring species becomes two distinct species.
• Formally, the issue is that interfertile " is not a transitive relation – if A can breed with B, and B can breed with C, it does not follow that A can breed with C – and thus does not define an equivalence relation. • A ring species is a species that
exhibits a counterexample to transitivity.
References• ^ Brown, Rob, "Same Species" vs. "Interfertile
": concise wording can avoid confusion when discussing evolution, http://karmatics.com/docs/evolution-species-confusion.html
• Alström, Per (2006): Species concepts and their application: insights from the genera Seicercus and Phylloscopus. Acta Zoologica Sinica 52(Supplement): 429-434. PDF fulltext
• Liebers, Dorit; de Knijff, Peter & Helbig, Andreas J. (2004): The herring gull complex is not a ring species. Proc. Roy. Soc. B 271(1542): 893-901. doi:10.1098/rspb.2004.2679 PDF fulltext Electronic Appendix
• Irwin, D.E., Irwin, J.H., and Price, T.D. (2001): "Ring species as bridges between microevolution and speciation." Genetica. 112-113: 223-243.
• Futuyma, D. (1998) Evolutionary Biology. Third edition. Sunderland, MA, Sinauer Associates.
• Moritz, C., C. J. Schneider, et al. (1992) "Evolutionary relationships within the Ensatina eschscholtzii complex confirm the ring species interpretation." Systematic Biology 41: 273-291.
