Effects of sex and reproductive mode on dietary composition of the reproductively bimodal scincid lizard,Lerista bougainvillii

4 Pages·1994·1 MB·English

by  Graeme Barden

Effects of sex and reproductive mode on dietary composition of
the reproductively bimodal scincid lizard, Lerista bougainvillii
Graeme Barden' and Richard Shine*
School of Biological Sciences A08, The University of Sydney, NSW 2006
*To whom correspondence should be addressed
'Present address: National Registration Authority for Agricultural and Veterinary Chemicals, P.O. Box 240,
Queen Victoria Terrace, Parkes, ACT 2600
We dissected preselved specimens from bath oviparous and viviparous South Australian popula-
tions of a fossorial skink Lerista bwgainvillii, to identify food items and to examine possible effects of
sex and reproductive mode on the composition of the diet. There were significant differences in dietary
composition (i) between the sexes and (ii) within each sex, between oviparous (Eyre Peninsula,
Fieurieu Peninsula) and vivioarous lKanaarw Island) mnsoecifics. In boUl woulations. females
tendedto feed prikarily on lGge, surface-;dive prey (prirnarii~h emipterans) raiher than the smaller,
s.e. c. re. t. iv. e. n ra-v, i, a-~--in-- l-,l vwe -e-v ils-), that hminntad the diets of m-ale.s.. This. ~diffe rence mav reflect
females' oiffc2,ties in penetraung Into narrow spaces under aver items: females ~a~re th~ e ,arger sex.
an0 are mnsaeraoly alstenoea oLnng geslat;on. Diets also dlfferea between oviparods and v v parobs
populations, in bath sexes, but these differences may reflect local resource availability rather than a
direct effect of reproductive mode. Our preliminary analysis suggests that a more detailed study of this
question would be worthwhile.
INTRODUCTION The evolution of viviparity has been a major
focus of research in reptilian biology for more
Reproductive biology and foraging ecology
than half a century (e.g., Weekes 1933; Tinkle
may influence each other in complex ways,
and Gibbons 1977; Shine 1985). Most
and squamate reptiles offer ideal model systems
evolutionary origins of viviparity have been
in which to investigate this interaction (e.g.,
followed by extensive adaptive radiations, so
Huey and Pianka 1981). For example, viviparity
that it is difficult to identify the morphological
(live-bearing) has arisen from oviparity (egg-
and ecological characteristics of the organisms
laying) at least 100 times within reptile
in which viviparity arouse. However, a small
phylogeny (Shine 1985). The evolution of
number of extant squamate species show both
viviparity within a reptile species might affect
oviparous and viviparous reproduction in
the animal's seasonal schedules of activity, and
different parts of their geographic ranges,
the greater distension of the female's body by
and hence offer uniquely suitable material
the offspring (Qualls and Shine, in prep.) may
with which to investigate the effects of this
restrict the range of microhabitats in which
major evolutionary transition. One such taxon
gravid lizards can forage. These kinds of shifts
is the elongate, fossorial xincid lizard Lmista
in the times and places that foraging occurs,
could well influence the composition of the bougainuillii of southeastern Australia (Fig. 1).
diet. The reverse phenomenon may also occur, Mainland populations in New South Wales,
whereby adaptations of foraging biology Victoria and South Australia reproduce by
modify the reproductive biology of reptiles egg-laying, but island p~~ulatiotrw~o asr~ca~s ~
(Vitt and Congdon 1978). For example, (Bass Straidl'asmania and Kangaroo Island)
ambush predation may facilitate the evolution bear fully-formed live young (~reer1 989;
of vivi~aritv. because the loneer eestation Qualls et al. 1994). The South Australian
" "
period'of vi"iparous lizards and the greater populations of L. bougainuillii are particularly
bodily distension of gravid live-bearers may well-suited to comparisons between egg-laying
be less of a "cost" to such species than to a and live-bearing conspecifics, because the live-
more elongate active forager that relied upon bearing animals on Kangaroo Island are
mobility for prey capture and predator escape separated by <20 km from egg-laying lizards
(Fitch 1970). Either causal pathway could of the same species on the Eyre and Flerieu
result in trophic differences between ovi- Peninsulas (Qualls et al. 1994). Morphological,
parous and viviparous female lizards, and electrophoretic and DNA-sequence studies
between females and conspecific males. have confirmed that the oviparous and
December 1994 Australian Zwlogist, Vd. 29(3-4) 225
RESULTS
First, we report body sizes of the lizards
from which prey items were identified. A
two-factor analysis of variance, with sex
and reproductive modes as the factors, and
snout-vent length (:SVL, in mm) as the
dependent variable, showed that there was
a highly significant difference in mean
body size between the sexes (F1,ss: 22.3,
P < 0.0001), but no overall difference in
body size between oviparous and viviparous
populations (Fr,so : 0.40, P : 0.53), and
Figure l. An adult Izrista bougainuillii (photo by C. Qualls). no difference in the degree of sexual size
Note the small head and limbs, and elongate body of this dimorphism between the two geographic areas
fossorial lizard. sampled (Fr,so: 0.02, P : 0.88). Combining
data from both areas,m ales (mean : 45.9 mm
viviparous populations within this speciesa re SVL, SD : 6.79) were much smaller than con-
closely related (Fairbairn 1993; Qualls et al. specificf emales (mean : 54.9 mm, SD : 4.57).
1994).
All of the prey items identified were
As is the case with most Australian lizard
invertebrates. The most important prey taxa
species (Greer 1989; but see Lunney et al.
numerically, in terms of total numbers of prey
1989), there have been no quantitative
as well as the numbers of lizards eating that
analyses of dietary habits in Izrista bougainuillii.
prey, were beetles (Coleoptera). These
We examined and identified gut contents of
constituted >40 per cent of the prey items
specimens from the area in South Australia
identified from each of our four groups of
where both reproductive modes occur, to
lizards, and )20 per cent of all prey-type
(i) describet he general diet of this species,a nd
(ii) examine the effects of gender and repro- occurrences within each group of lizards
(Table 1). Within the Coleoptera, the
ductive mode on the kinds of prey items
Curculionidae (weevils)w as the most important
consumed.
taxon (>20% of prey items in each group,
>20% of prey-occurrence records). A single
MATERIALS AND METHODS
species of weevil of the genus Sclerorinusw as
The lizards we used for these analysesw ere the major contributor to these numbers, con-
preserved specimensi n the collections of the stituting > 16 per cent (and tp to 47 %) of prey
Australian Museum and South Australian items within each group of lizards, and )19
Museum. The lizards examined ranged from per cent (up to 26%) of prey-occurrence
32 to 62 mm snout-vent length. All of the records. The next most important group were
viviparous animals (n : 9 males, 4 females) bugs (Hemiptera), especiallyi n female rather
came from Kangaroo Island, and the egg- than male L. bougainuillii (Table l). Most other
layers (n : l5 males, 17 females) came from groups of invertebrates were taken only rarely,
the nearby Eyre Peninsula (n : 28) and although lizards from Kangaroo Island con-
Fleurieu Peninsula (n : 4). The gut contents tained significant numbers of pseudoscorpions
were removed through a midventral incision, (Table 1).
and then identified using available taxonomic
keys. The resultant data are shown in Table Our two methods of scoring importance
1, which presents the data separatelya ccord- generally yielded similar results, although
ing to sex and reproductive mode of the some differences were apparent. For example,
lizards. We estimated the importance of each coleopterans constituted 73 per cent of all
prey taxon in two ways: as a proportion of all prey items from mainland male lizards, but
prey items found in that group of lizards only 52 per cent of prey-occurrence records
(sorted by gender and reproductive mode - from this group (Table l). This difference
e.9., males of the oviparous populations), and reflects a tendency for multiple meals: lizards
as a proportion of all prey-occurrence records with coleopterans in their stomachs had often
in lizards in that group (so that multiple prey eaten several specimens. Contingency-table
items within a single lizards counted as only tests were used to compare the relative
one record). The latter method reducesb iases frequences of different prey types between
that can arise if a few individuals contain very sexes and between reproductive models (we
large numbers of a particular prey type. did not compare prey-occurrence categories
226 AustraliaZno ologistV, ol.2 9(3-4) December1 994
because sample sizes were too low for adequate the stomach contents in this species. Our
statistical power). Results were as follows: subjective impression from bites incurred
(i) Gender. Males and females differed in when handling live animals, is that the
dietary composition in the oviparous jaws of Lerista bougainuillii are far more
(mainland) population (X2 = 38.1, 10 df, powerful than are those of similar-sized
P < 0.001). A similar difference between skinks such as Lampropholis or Murethia.
the sexes was evident in the viviparous In particular, the prevalence of weevils
population, but the lower sample size (Curculionidae) is a tribute to the power-
meant that this difference did not attain ful jaws of these tiny lizards. Weevils are
statistical significance (x2 = 19.8, 13 df, exceptionally hard-bodied prey and we
P = 0.10). suspect that most small skinks of other
species would by unable to crush their
(ii) Reproductive mode. Because of the signifi-
exoskeletons. Although some weevils had
cant sex difference documented above, we
been swallowed entire or had been
analysed data separately for the two sexes.
broken into discrete body segments
Significant differences between oviparous
(along existing suture lines), rather than
and viviparous opulations were evident
in both males (xB= 36.6, 14 df, P < 0.001) crushed, close examination of ingested
and females (x2 = 51.5, 9 df, P < 0.001). weevils showed that their sclerites were
usually cracked.
DISCUSSION (ii) The breadth of the diet suggests that L.
bougainvillii are relatively unselective with
Our data set is preliminary in nature,
respect to the prey items they will eat,
because it is based on very small sample sizes
and that these lizards forage in a variety
collected over a long time period. Nonethe-
of microhabitats. In this respect L.
less, the data in Table 1 are sufficient to reveal
bougainvillii resemble other small Austra-
some interesting trends.
lian skinks such as Lampropholis guichaoti
(i) The relatively high proportion of prey and L. deliceta (Lunney et al. 1989). The
items unidentifiable to the familial level coleopterans ingested are probably taken
reflects the well-macerated condition of mostly under cover items, where they
Tabk I. Prey items identified from stomach contents of semi-fossorial scincid lizards, Lnirto bougamvillii from South Australia.
The table provides data on the number of prey items (absolute values, and as a percentage of all prey items identified from
that group of lizards) and on the number of lilards containing they prey type (absolute numben, and as a percentage of all
prey-type occurrences of lizards within that group). Common names from Naumann (1993).
By number of prey items: By number of lizards:
Oviparous Viviparous Oviparous Viviparous
Prey taxon Common name male female male female male female male female
Coleoptea beetles 36 (73%) 48 (46%) 14 (45%) 5 (42%) 12 (52%) 14 (48%)
Currulionidae weevils 29 (59%) 34 (32%) 7 (23%) 3 (25%) 8 (35%) 9 (31%)
Cantharidae soldier beetles 0 7 (7%) 1(3%) 0 0 1(3%)
Cryptophagidae 0 0 I(?.%) 0 0 0
Ch~wmelidae leaf beetles 1(2%) 1(1%) 0 0 1(4%) I@%)
Cucujidae (larvae) 0 0 2 (6%) 0 0 0
Unidentified 6(12%) 6 (6%) 3 (10%) 2 (17%) 5 (22%) 6(22%)
Hemiptea bugs 6(12%) 54(51%) 1(3%) 6(50%) 2 (9%) 9(31%)
Cydnidae burrowing bugs 0 0 1(3%) 1(8%) 0 0
Pentatornidae shield bugs 6 41 (39%) 0 1(8%) 2 (9%) 7 (24%)
Lygaeidae reed bugs 0 12(11%) 0 0 0 2 (7%)
Unidentified 0 I(l%) 0 4(33%) 0 1(3%)
Other Insecta
Formicidae ants 1(2%) 3 (3%) 1(3%) 0 1 (4%) 2(7%) 1(5%) 0
Lepido~tera( pupae) caterpillan 0 0 2 (6%) 0 0 0 1(5%) 0
Thysanoptera thrips 0 0 2 (6%) 0 0 0 2 (10%) 0
Unidenaed 2 (4%) 0 1(3%) 0 2 (9%) 0 1(5%) 0
Arachnids
Pseudworpiones preudo~mrpions 0 0 7 (23%) 1 (8%) 0 0 4 (19%) 1 (22%)
Amnei& apiden 1(2%) 0 0 0 1(4%) 0 0 0
MoUusca
Gastmpoda snails 3 (6%) 0 3 (10%) 0 1(4%) 0 1(5%) 0
Touls 49 105 31 12 23 29 21 9
December 1994 Australian Zoologist, Vol. 29(&4) 227
hide, but the hemipterans are more likely to populations of L. bougainvillii, especially
be taken when they are active, in more open between the viviparous Bass Straiflasmanian
habitats. These powerful fast-moving skinks animals and their nearest oviparous (Victorian)
probably have little difficulty in overpowering conspecifics. It should also incorporate
even formidable prey such as spiders. measurements of prey availability in the
different habitats, to allow an assessment of
(iii) The consistent tendency for female L.
the degree to which geographic differences in
bougainvillii to take more hemipterans
dietary composition reflect some attribute of
than do males (in both oviparous and vivi-
the study animal (e.g., reproductive mode)
parous populations: Table 1) may reflect
versus a direct influence of geographic
either size selection (hemipterans tend to
differences in prey availability.
be larger than coleopterans) or, more
likely, differences between the two sexes
in foraging microhabitats. Females are ACKNOWLEDGEMENTS
larger than males in this species (see
We thank A. E. Greer (Australian Museum)
above) and hence may take larger prey:
and M. Hutchinson (South Australian
such a correlation has been documented
Museum) for allowing us to dissect specimens
in many other types of reptiles (e.g.,
in their care, C. Qualls for insights into the
Shine 1991). Alternatively, the sexes may
biology of Lekta bougainudlii and the Austra-
diverge in foraging microhabitats, if the
lian Research Council for financial support.
larger females are less able to fit under
close-fitting cover objects to take coleop-
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