Biology Reference
In-Depth Information
distribution between 35 and 47°N (Holcík, 1986; Holcík and Renaud, 1986;
Renaud, 1986). Potter et al. (1980) showed the month variation of the onset
of metamorphosis in
G. australis
from January in southern Tasmania (43°S
latitude, 147°E longitude) to early February in southwestern Australia (34°S
lat., 116°E long.) There are also examples within species where altitude
infl uences the seasonal onset of metamorphosis (Hardisty, 2006). For an
extended discussion and interesting speculation on how altitude, latitude
might infl uence the timing of metamorphosis and water temperature we
recommend Hardisty (2006).
Potter (1970) was among the fi rst to show, through laboratory experiments
with
M. mordax
, that metamorphosis occurs earlier in larval lampreys
exposed to the higher of two water temperatures. This evidence along with
the reports of earlier metamorphosis of
L. planeri
and
L. fl uviatilis
following
an early spring (Bird and Potter, 1979a) and the consistent correlation of
metamorphosis in the anadromous sea lamprey (
P. marinus
) with the breakup
of ice in the St. John River system in New Brunswick, Canada (Potter and
Beamish, 1977), led Potter (1980) to suggest that the onset of metamorphosis
is more related to a pattern of change rather than the reaching of an optimum
water temperature. If there is a critical temperature to initiate metamorphosis
and it varies among populations of the same species, the variation in the
time of initiation could be a consequence of differences in their exposure to
annual temperature regimes (Potter et al
.
, 1982).
The importance of water temperature to lamprey metamorphosis
has been explored through extensive laboratory studies on larvae of the
landlocked sea lamprey (
P. marinus
). These studies have been recently
reviewed by Youson (2003) and there have been no other studies since this
review. The reader is referred to this most recent review and, herein, we will
highlight the most salient points coming from the individual investigations.
Purvis (1980) conducted fi eld and laboratory studies without intra- and
inter-experimental controls to show 75 to 100% metamorphosis of animals
housed at 20 to 21°C, 46-76% at 14 to 16°C, and 5 to 10% at 7 to 11°C and
concluded that controlled laboratory experiments were needed. The fi rst of
these subsequent laboratory experiments (Youson et al
.
, 1993) showed that
when animals of uniform size (common masses and lengths) are subjected
to water temperatures of either 13 or 21°C on June 10-11 a signifi cantly
higher incidence of metamorphosis occurs at the higher temperature in
the following month, the normal month for metamorphosis. In this study
that was duplicated over two years, there was a much higher incidence
of metamorphosis at both temperatures in the second year (overall 76%
compared to 11.2% in year 1) when the animals were at least 120 mm long
and weight at least 3.0 g. The incidence of metamorphosis was 66% at 13°
and 84% at 21°C but development was much slower and even suppressed
at the lower temperature in both years of the study. Although this was
