Fj. Janzen et al., INFLUENCE OF THE HYDRIC ENVIRONMENT AND CLUTCH ON EGGS AND EMBRYOS OF2 SYMPATRIC MAP TURTLES, Functional ecology, 9(6), 1995, pp. 913-922
1. Substrate moisture exerts substantial yet variable effects on the p
hysiological ecology of reptilian eggs and embryos. Although previous
studies have focused on one species at a time, simultaneous comparativ
e examinations can lend greater insight into the functional significan
ce of this variation by allowing direct quantitative, as opposed to in
ferred, comparisons. 2. We concurrently incubated eggs of two syntopic
, congeneric turtles (Graptemys ouachitensis and G. pseudogeographica)
at 29 degrees C on 'wet' (-150kPa) and 'dry' (-950kPa) substrates to
assess the effects of substrate moisture on growth and survivorship of
embryos. 3. Water potential did not influence embryonic mortality or
hatchling abnormalities but small eggs were less likely to hatch than
large ones. 4. Eggs of both taxa gained mass, took longer to hatch and
produced larger hatchlings when incubated on the wet substrate compar
ed to the dry substrate. These physiological traits were also influenc
ed by clutch and taxon, suggesting possible genetic variation. 5. Eggs
of G. ouachitensis gained relatively more mass at -150kPa, lost relat
ively less mass at -950kPa and hatched sooner than did eggs of G. pseu
dogeographica. Hatchling G. ouachitensis were relatively larger than h
atchling G. pseudogeographica and this taxon effect was greater than t
he influence of the hydric environment. 6. Significant quantitative di
fferences in the physiological responses of the two taxa to substrate
moisture support recent taxonomic work suggesting that they are separa
te species. Detection of and confidence in these differences were only
possible because eggs were incubated simultaneously.