Understanding why organisms possess certain combinations of life-history traits is
important to our understanding of how natural selection operates. Combinations of life-history
traits evolve in response to the costs of current reproduction to both survival and
future reproduction. Reproductive costs have been broadly categorised into two types: 1)
survival costs, and 2) potential fecundity costs. As a means of predicting and explaining
variation in reproductive investment in lizards and snakes, Shine and Schwarzkopf (1992)
attempted to determine the relative importance of the two kinds of costs to individual
lifetime fitness (the SS model). They concluded that most lizard species are unlikely to
make trade-offs between current and future reproduction (fecundity costs). In this study
of a temperate-zone lizard, Elgaria coerulea, I have three main objectives: 1) to provide
the first natural history data for a Canadian population of this species, 2) to describe life-history
traits for this population, and 3) to formally test the predictions of the SS model
and discuss its potential predictive power.
Individual Elgaria coerulea occupy relatively small areas, thus minimising costs associated
with a long-distance migration. In addition to having limited movement, Elgaria
coerulea rely on hiding as one of their main anti-predator strategies, although there is
sex-dependent variation in their retreat-site selection. Emergence patterns of male Elgaria
coerulea did not change over their reproductive cycle. In contrast, the probability of capturing
an adult female in the open steadily increased over the summer. These results suggest
that the benefits of emerging from cover outweigh the costa in females, but not males.
Annual survival rate of adult females was 44% and juvenile survival rate was 22%.
The survival rate of adult males likely fell in between these values, but I was not able to
estimate it directly because of small sample sizes. I infer from the female’s relatively high
survival rate that the necessity for gravid females to spend more time in the open during
gestation does not translate simply to increased mortality.
Gravid females have reduced sprint speed and sprint speed was inversely related
to the burden of the clutch. Therefore, gravid females presumably could reduce their
predation risk by remaining closer to cover than males or juveniles. However, this is not
the case; all northern alligator lizards remained close to cover. Thus, the lack of shift in
anti-predator behaviour of gravid females may be a result of all Elgaria coerulea relying on
crypsis rather than sprinting as an anti-predator defence. I did detect a difference in body
coloration. Gravid females had more black pigmentation than males or juveniles. The black
pigmentation may help females blend in with their background better than males, thereby
reducing predation risk, or help increase their body temperature at a quicker rate.
Another important anti-predator strategy in Elgaria coerulea is tail autotomy, and
once again I measured variation in this trait between males and females. Gravid females
never lose small parts of their tails, perhaps giving them extra time to escape from a
predator. Furthermore, recent tail loss was not seen in gravid females during late gestation.
By contrast, males were equally likely to autotomise at any time of the year. Females
may be less likely than males to lose their tails because of the potential reproductive gain
by females with intact tails. Females with intact tails had a higher probability of being
reproductive and females with longer tails had larger newborn.
Finally, I show that some Elgaria coerulea trade current reproduction for growth.
Examination of reproductive costs in Elgaria coerulea revealed problems with incorporating
cold-climate reptile species into the SS model. Because cold-climate species spend significant
time in hibernation each year they have relatively short interclutch intervals. For these
species the SS model predicts that trade-offs between current and future reproduction are
more likely. The likelihood of fecundity costs also increases, even that concurrent growth
and reproduction may be more prevalent than previously believed, as is evident in Elgaria
coerulea. Both of these factors need to be incorporated into the SS model is increase our
ability to make predictions about the evolution of reproductive effort in cold-climate species. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/10250 |
| Date | 02 November 2018 |
| Creators | Rutherford, Pamela |
| Contributors | Gregory, Patrick T. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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