Abstracts
Schappert, P. J. and J. S. Shore, 1995.
Cyanogenesis in Turnera ulmifolia L. (Turneraceae). 1. Phenotypic
distribution and genetic variation for cyanogenesis on Jamaica. Heredity 74:
392-404.
A survey of 39 discrete populations of Turnera ulmifolia on Jamaica reveals extensive phenotypic variation for cyanogenesis among populations. The variation is quantitative and appears to be the result of differences in the quantity of cyanogenic glycosides possessed by plants. Controlled crosses and greenhouse studies show that there is a genetic basis to the variation with between-family variance accounting for more than 80% of the variation in one population. Seedlings have significantly higher levels of cyanogenesis than mature plants in largely acyanogenic populations but this age-specific variation is absent in predominately cyanogenic populations. We identify potential selective agents that might account for the spatial distribution of cyanogenesis on the island and discuss the geographical pattern with respect to population elevation, precipitation regimes and the distribution of herbivores. This investigation provides the first detailed study of the ecological genetics of cyanogenesis in natural populations of a tropical plant.
Schappert, P. J. and J. S. Shore, 1998. Ecology,
population biology and mortality of Euptoieta hegesia Cramer
(Nymphalidae) on Jamaica. Journal of the Lepidopterists’ Society 52: 9-39.
We examine the ecology, population biology and
potential sources of mortality of Euptoieta hegesia, a tropical lowland
butterfly from Jamaica, using a combination of captive rearing, studies of
natural populations, and experimental approaches. We provide detailed
observations of the life cycle and methods for captive rearing of this species.
We assess the relative performance of larvae on primary and secondary host
plants, distribution of larvae on primary the host plant, host plant population
utilization, and the distribution of E. hegesia on the island. A
mark-release-recapture study was conducted to estimate population parameters
and we recorded sex, size, age (as estimated by wing wear), and the wing damage
sustained by the butterflies prior to their initial capture. We provide
evidence that Turnera ulmifolia is the primary host plant of E.
hegesia on Jamaica and that butterfly population size is not limited by the
availability of host plants. These short-lived butterflies appear to be
residents of discrete host plant populations and experience high mortality
levels. Females are damaged more frequently; show more total damage, and more
frequent symmetrical hindwing damage (attributable to ground-based predators)
than do males. We compare the results of the population study with available
studies of other tropical butterflies and suggest that lowland butterfly
population structure and dynamics are significantly different from that of
rainforest species.
Schappert, P. J. and J. S. Shore, 1999. Effects
of cyanogenesis polymorphism in Turnera ulmifolia on Euptoieta
hegesia and potential Anolis predators. Journal of Chemical Ecology
25: 1455-1479.
We examine the effects of the cyanogenesis
polymorphism in Turnera ulmifolia on larvae, pupae and adults of Euptoieta
hegesia, the most damaging herbivore of T. ulmifolia in terms of
tissue loss per unit time. We provide evidence that female E. hegesia do
not show preference for host plants on the basis of their cyanogenesis but do
prefer T. ulmifolia over equally cyanogenic, closely related secondary
host plant species (Passiflora sp.). Similalry, cyanogenesis in T. ulmifolia
has little effect on the food preference, growth, or development of the larvae.
The potential host range of E. hegesia is limited, even within the genus
Turnera, but this does not appear to be due to host plant cyanogenesis.
Pupae suffer very high mortality levels in the wild that are not associated
with host plant cyanogenesis, although our studies indicate that larvae are
capable of sequestering cyanogenic glycosides from their host plants and
possibly of synthesizing these or similar compounds. We provide evidence that
the presence of sequestered cyanogenic compounds in the larvae protects them
from terrestrial-based predators such as Anolis lizards.
Schappert, P. J. and J. S. Shore, 1999.
Cyanogenesis, herbivory and plant defense in Turnera ulmifolia on
Jamaica. Ecoscience 6: 511-520.
Field surveys of 8 populations of Turnera
ulmifolia L., a Jamaican weed exhibiting quantitative genetic variation for
cyanogenesis, were undertaken to assess the effectiveness of cyanogenesis as a
plant defense. Populations known to be characteristically acyanogenic,
cyanogenic, or exhibit within-population variation were surveyed for
cyanogenesis, plant size, and the presence and identity of invertebrate plant
visitors. A developmental series of 10 leaves from a shoot of each surveyed
plant was analyzed, using image analysis techniques, for the type and extent of
damage present. We also surveyed two additional plant populations for the
presence of plants with eggs or larvae of Euptoieta hegesia Cramer, a
Nymphalid butterfly that is potentially the most damaging herbivore of T.
ulmifolia, and a paired comparison analysis of cyanogenesis in plants with
the herbivore versus plants without the herbivore was conducted. We found that T.
umifolia are attacked by a reasonably diverse insect fauna, but a
relatively small suite of specialist herbivores that are seemingly undeterred
by cyanogenesis inflicts most of the leaf damage. Cyanogenesis does appear to
play a role in determining the types, numbers, and presence of generalist
herbivores found within and between populations; however, the proportion of
leaf tissue lost due to herbivory is low, ranging from only 1-9% on average,
and does not appear to be correlated with cyanogenesis in a consistent way. An
analysis of covariance did, however, reveal that cyanogenesis has a significant
effect on both plant height and number of shoots per plant. These results
suggest that cyanogenesis might afford protection against herbivory from
generalizing herbivores.
Schappert, P. J. and J. S. Shore, 2000.
Cyanogenesis in Turnera ulmifolia L. (Turneraceae). 2. Developmental
expression, heritability and cost of cyanogenesis. Evolutionary Ecology
Research 2: 337-352. (paper PDF)
We examine the cyanogenesis polymorphism in Turnera ulmifolia on Jamaica with respect to our hypothesis that seedlings in some populations have significantly higher levels of cyanogenesis than mature plants because of the developmental loss of cyanogenesis. Furthermore, we provide estimates of among-family variance, as estimates of broad sense heritability, for a number of fitness-related traits, and also examine the potential cost of cyanogenesis in this species. Our data reveal that there is a marked developmental loss of cyanogenesis in some populations of T. ulmifolia. Seedlings have significantly greater levels of cyanogenesis than mature plants in “acyanogenic” populations, but this developmental loss is absent in predominately cyanogenic populations. This is the first study to document extensive developmental loss of chemical defense in a cyanogenic species. We suggest that, in these populations, there might be selection favoring cyanogenesis in seedlings. There is substantial among-family variance in a number of traits in five T. ulmifolia populations examined, including plant height, time to first flowering, total flower production and cyanogenesis. Phenotypic and, more importantly, negative genetic correlations between total flower production and cyanogenesis provide evidence for a cost of cyanogensis in three of five populations.