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Some Challenging Questions in
New England
Odonata
Nick Donnelly
Abstract:
In Enallagma, two species appear to be intergrading
widely:
Northern Bluet
(E. cyathigerum) and Vernal Bluet (E. vernale). In the
Northeastern part of the
US
and adjacent
Canada
(
Michigan
to
Nova Scotia
and south to
Pennsylvania
, cyathigerum is almost invariably a bog species, avoiding habitats with
a significant fish population. E. vernale, on the other hand, is found in
medium-sized rivers and lakes, commonly with abundant fish. However, both
species wander from their preferred habitats and evidently intergrade - that is,
hybridize, but produce fertile offspring. Typically, specimens of cyathigerum
taken together at a single time range morphologically between the two end
members. Enallagma vernale is scarcer, but populations again show
morphological variation. In the remainder of its broad range (west from
Wisconsin
to the west coast and north to
Alaska
) cyathigerum inhabits almost all aquatic habitats. How did it become
restricted to fishless habitats in the northeast? We need more observations,
especially occurrences in
Massachusetts
, where it has been reported far less than in
New York
.
The genus Tetragoneuria
provides another, very different, challenge. In easternmost
Massachusetts
the common species seems to be semiaquea, but it has unmarked wings and
is easily confused with cynosura. From
Long Island
southward semiaquea has broad wing markings, except that in
New Jersey
a minority have deeply reduced maculation. The challenge is to find if the two
species co-occur in
Massachusetts
, and, if so, do they show differences in behavior and/or habitat.
Biography: Nick Donnelly has been studying odonates
across North American and the world for over half a century, and is one of the
world’s pre-eminent odonatologists. He was one of the founding members of the
Dragonfly Society of the
Americas
and edits their newsletter, Argia. He has published scores of papers
about odonates worldwide, and is currently working on a guide to North American
Odonata.
Contact Info: T. W. Donnelly,
2091 Partridge Lane
,
Binghamton
,
NY
13903
. Email: tdonelly@binghamton.edu
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