Keywords
body size, variation, discontinuity, phenotypic plasticity, dimorphism
Introduction
Luciola parvula(Coleoptera, Lampyridae) is a terrestrial firefly species widely
distributed in Japan and shows large geographical variation in adult
body size especially in mountainous areas. Previous studies reported
that there were two ecological morphs of adults of this species: large
and small morphs. However, the procedure used to identify the two morphs
has remained ambiguous and confused. Therefore, the present article
begins with a brief review of the two morphs in this species and then
proposes an allometric approach to detect the existence of the two
morphs.
As far as the present author knows, Ohba (1) was the first to describe
the criteria for the classification of the two morphs in this species.
He collected male adults at Mt.
Hakone, central Japan and then
identified the large morph above
700 m altitude and the small
morph below this altitude. He also reported that the approximate body
length was 10 mm for the large morph and 6 mm for the small morph.
Ohba (2) further examined male
adults of this species throughout Japan and then found the large morph
with body length 7 to 9 mm and
pronotum width larger than 2.1 mm and the small morph with body length 5
to 7 mm and pronotum width smaller than 2.1 mm.
Mitsuishi
(3–6) collected
male adults of this species at 41
sites in Nagano Prefecture, central Japan and classified them into the
large morph (body length larger than 8 mm) and the small morph
(body length approximately 7 mm).
Aa a result, he found that this species in this prefecture tends to be
segregated into a northeastern and a southwestern group corresponding to
the large and the small morph, respectively, but that both morphs exist
above 1000 m altitude. However,
these findings were not consistent with Ohba’s findings (1). This may be
partly due to the arbitrariness of the criteria for the two morphs.
Ohba (7) reviewed his studies on the two morphs of this species and
summarized his criteria for the classification of
them: the large morph with body
length 7 to 8 mm below 1600 m altitude and the small morph with
body length 5 to 6
mm below 800 m altitude.
Kusaoke et al. (8) investigated
the distribution of this species in Toyama Prefecture, adjacent to
Nagano Prefecture mentioned above and found the small morph (body length
approximately 6 mm) at three sites at altitudes of 400 to 700 m and the
large morph (body length approximately 8 mm) at an altitudes of 1100 m.
As they mentioned, these findings almost fell into
Ohba’s criteria (7). Therefore,
they considered that Mitsuishi (3–6) had found only the large morph
above 1000 m altitude in Nagano Prefecture.
However, Kusaoke et al. (8) also found at Mt. Daisen, Tottori
Prefecture, that the large morph (mean body length 8.12 mm) exited at
1709 m altitude and small morph (mean body length 7.14 mm) at 800 m
altitude. These mean values of body length were not consistent with
Ohba’s criteria (7).
In these studies, this species was more or less arbitrarily classified
into the large and small morphs. No statistical analysis was performed
to examine whether or not body size varies continuously.
Molecular phylogenetic studies suggested that the small morph originated
from an ancestor similar to the large morph (9, 10). However,
no genetic difference was found
between the two morphs at Mt. Daisen, Tottori Prefecture (8).
Ohba (7) also showed that the flash interval (0.5 to 0.6 s) of the
small morphs is smaller than that (0.7 to 0.8 s) of the large morph.
However, he did not take into consideration the effect of temperature on
flash intervals. In fact, such temperature effects were found and
statistically analyzed in Nipponoluciola cruciate (formerlyLuciola cruciate ) (11–13). Therefore, it remains unclear whether
the two morphs of this species show different flash intervals under
controlled temperature.
Regarding morphological measurements of L . parvula , the
previous studies focused on simple descriptive statistics such as mean
values of body length. However, multivariate analyses are considered
necessary for detecting size dimorphism in this species. Therefore, the
existence of inconsistent criteria for the two morphs of this species
leads the present author to reexamine published data on measurements of
this species.
Fortunately, Mitsuishi (3–6) showed his measurement data on body
length, body width and pronotum width at 41 sites in Nagano Prefecture.
Using these data, the present article attempts to detect differences in
scaling relationships between the two morphs by allometric analysis. The
results will help to provide direction for future studies on the size
dimorphism of this species.