[MARMAM] New publications on killer whale evolutionary ecology

Andy Foote footead at gmail.com
Thu Aug 15 23:56:06 PDT 2013

Dear colleagues,

Two papers on the evolution of killer whale types and forms have just been
published online:

Mitogenomic insights into a recently described and rarely observed killer
whale morphotype
Andrew D. Foote, Phillip A. Morin, Robert L. Pitman, Maria C. Avila-Arcos,
John W. Durban, Anton van Helden, Mikkel-Holger S. Sinding and M. Thomas P.
Polar Biology, DOI 10.1007/s00300-013-1354-0

Identifying evolutionary divergent taxonomic units, e.g. species and
subspecies, is important for con- servation and evolutionary biology. The
‘type D’ killer whale, Orcinus orca, is a rarely observed morphotype with a
pelagic, circumpolar subantarctic distribution, making dedicated research
and therefore taxonomic study extremely difficult to date. In this study,
we used DNA target enrichment hybridisation capture coupled to high
throughput sequencing, to obtain the first DNA sequence from the only known
museum specimen of this recently described morphotype. The high coverage,
complete mitogenome sequence was compared to a previously published global
dataset of 139 individuals, indicating that this type is highly divergent
to all previously genetically sequenced killer whale forms. The estimated
divergence time (390,000 years ago) from its most recent common ancestor
with other extant killer whale lineages was the second oldest split within
the killer whale phylogeny. This study provides the first genetic support
of type D potentially being a distinct subspecies or species of killer
whale, although further samples are needed to identify whether there is
monophyly of mitogenome sequences and whether nuclear DNA also indicates
reproductive isolation. These findings also highlight the value of natural
history museum collections and new technologies to investigate the taxonomy
of rare, cryptic or difficult to access species.

Tracking niche variation over millennial timescales in sympatric killer
whale lineages
Andrew D. Foote, Jason Newton, Maria C. Avila-Arcos, Marie-Louise Kampmann,
Jose A. Samaniego, Klaas Post, Aqqalu Rosing-Asvid, Mikkel-Holger S.
Sinding and M. Thomas P. Gilbert
Proceedings of the Royal Society B, 280: 20131481

Niche variation owing to individual differences in ecology has been
hypothesized to be an early stage of sympatric speciation. Yet to date, no
study has tracked niche width over more than a few generations. In this
study, we show the presence of isotopic niche variation over millennial
timescales and investigate the evolutionary outcomes. Isotopic ratios were
measured from tissue samples of sympatric killer whale *Orcinus
orca*lineages from the North Sea, spanning over 10,000 years. Isotopic
spanned a range similar to the difference in isotopic values of two known
prey items, herring *Clupea harengus* and harbour seal *Phoca vitulina*.
Two proxies of the stage of speciation, lineage sorting of mitogenomes and
genotypic clustering, were both weak to intermediate indicating that
speciation has made little progress. Thus, our study confirms that even
with the necessary ecological conditions, i.e. among-individual variation
in ecology, it is difficult for sympatric speciation to progress in the
face of gene flow. In contrast to some theoretical models, our empirical
results suggest that sympatric speciation driven by among-individual
differences in ecological niche is a slow process and may not reach
completion. We argue that sympatric speciation is constrained in this
system owing to the plastic nature of the behavioural traits under
selection when hunting either mammals or fish.

best regards,
Andy Foote and coauthors


*Dr Andrew Foote*
*Centre for GeoGenetics*
The Natural History Museum of Denmark
Øster Voldgade 5 - 7
1350 Copenhagen K
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