Two giant coots are known from New Zealand,
Fulica chathamensis chathamensis from the Chatham
Islands (Forbes 1892) and F. c. prisca from the mainland
(Hamilton 1893). The reliability of the depth of the
brachial depression of the humerus as a distinguishing
osteological character described by Olson (1975) was
questioned by Millener (1980), who described alternative
characters which he considered sufficient to
designate the two forms as species. The present genetic
analysis confirms the close relationship of the two
flightless coots, as they were found to have identical
12S gene sequences. However, only two nucleotide
substitutions separate them from the much smaller,
volant coot, Fulica atra australis. Although the result is
consistent with the proposal that the two flightless
forms were derived one from the other (Olson 1975),
the two giant coots which existed on islands separated
by over 500 km of sea are likely to have been
independently derived from the same ancestor. The
evolution of flightlessness and gigantism would presumably
have precluded subsequent dispersal
(Millener 1991).
Fulica atra stock are present in the recent fossil record
of Australia (Olson 1975) but not New Zealand and
have apparently invaded New Zealand on more than
one occasion without establishing permanent populations.
Indeed, the F. atra DNA sample used in this
study came from an individual caught in New Zealand,
which was probably a descendant of a recent (circa
1958) colonization event (Small & Soper 1959).
Comparison of 12S sequences from the coots and a
moorhen (Gallinula chloropus) indicates that both of the
substitutions which differentiate F. c. chathamensis prisca
from F. atra were probably derived in the volant F. atra.
If so, this suggests that morphological evolution of the
flightless coots in New Zealand was recent and
therefore probably rapid, and presumably occurred in
two parallel events. The New Zealand giant coots were
not unique and there is evidence that an equivalent
pair of giant Fulica species evolved on the islands of
Mauritius and Reunion in the Indian Ocean
(Greenway 1967; Olson 1977).
www.journals.royalsoc.ac.uk/media/M35EAC0C710TWLCD0N5U/Contributions/U/4/7/X/U47XY1WVJ8BPL737.pdf
