Water and Skin: Evolution of Cutaneous Water Barriers and its Implications for Biodiversity
Harvey B. Lillywhite
Department of Zoology, University of Florida, Gainesville, Florida 32611 U.S.A.
Lipids are widely used for increasing water resistance of terrestrial organisms including plants, arthropods, and vertebrates. Hence, cutaneous lipid barriers are important for niche diversification and the occupation of arid and semi-arid habitats. Examples and correlates of physiology with biodiversity can be illustrated from recent studies of amphibians, reptiles, and birds. The delicate, pliable nature of amphibian integument and its limited potential for keratinogenesis appear to constrain the evolution of possible waterproofing mechanisms within the Amphibia. Because of limitations in the expression of keratinized tissue, external lipid barriers structured by wiping behaviors seem to provide the more effective available means of waterproofing in extant amphibians. New comparative data from studies of arboreal frogs indicate components of wiping behaviors used to “layer” the external lipids of so-called “waterproof” frogs have a broader phylogenetic distribution than formerly supposed. Moreover, the secretion of lipids from both mucus and granular glands broadens our perspective of secretory mechanisms and water barrier evolution. The complex wiping behaviors of “waterproof” phyllomedusines appear to be an evolutionary refinement of behaviors that were probably present before lipids were involved in significant modifications of skin resistance. In contrast with amphibians, the successful diversification of reptiles in arid habitats was made possible by the evolution of effective “lipid/keratin complexes” present in reptilian epidermis. On the other hand, thermoregulatory requirements for evaporative water loss associated with endothermy potentially complicates the evolution of cutaneous lipid barriers in birds.
Experimentally Testing Evolutionary Models of Temperature Adaptation
Albert F. Bennett and Richard E. Lenski
University of California, Irvine & Michigan State University
Of particular interest at this time are evolutionary responses to global climate change, because of its potential effects on species' distributions and biodiversity. Many predictive evolutionary models make explicit or implicit assumptions about their pattern of those responses, including such factors as tradeoffs, niche shifts, and cross resistance to stressful environments. Many of these assumptions are directly testable using experimental evolutionary systems. Here we utilize different lineages of bacteria adapted to constant and varying temperatures to test fundamental issues of adaptation to the thermal environment.
Supported by NSF Grant IBN-9905980.
L.J. Chapman
University of Florida, USA
The introduction of predatory Nile perch (Lates niloticus) into
the Lake Victoria basin of East Africa coincided with the decline or disappearance
of hundreds of fish species, including many endemic haplochromine cichlids.
This faunal collapse led scientists to try to identify refugia where fishes
are protected from Nile perch predation. We have demonstrated that wetlands
protect some fishes from Nile perch predation by providing both structural
and low oxygen refugia for prey that can tolerate the oxygen-scarce conditions
that prevail in the dense swamp interior. Hypoxia poses a challenge for
non-air-breathing organisms; and thus, many fishes surviving in dense
wetlands are air breathers. However, in our studies of hypoxia tolerance,
we have found relatively high tolerance to low oxygen in some haplochromine
cichlids and other non-cichlids (e.g., large gill surface area, low critical
oxygen tension), and relatively low tolerance in Nile perch. This helps
to explain why some indigenous species persist in wetland refugia and
why Nile perch are unable to exploit these habitats. The remnant populations
of surviving species are extremely important because they are the seeds
of resurgence. In some areas of the Lake Victoria basin, overfishing has
reduced numbers of large Nile perch and sparked a resurgence of indigenous
species. However, these are biologically filtered faunas, representing
species that have persisted with Nile perch and have the flexibility to
respond quickly to reduced predator pressure.
Some of these species have experienced several generations of strong selection
pressure for the extreme conditions of the swamp environment and may therefore
differ morphologically and physiologically from their conspecifics that
lived during the pre-Nile perch phase. Our first series of data quantifying
change in the characteristics of recovering species in response to selection
pressure in faunal refugia supports the role of swamps in promoting diversification.
Claude Grenot and Sébastien Longepierre
Laboratoire Fonctionnement et Evolution des Systèmes Ecologiques, CNRS-UMR 7625, Ecole Normale Superieure, 46 rue d'Ulm F-75 230 Paris Cedex 05, France
Hermann's tortoise, Testudo hermanni hermanni (Thh), listed as
a threatened species, inhabits shrub desert (matorral) and open forest
in southern France. These populations have a highly fragmented distribution.
The tortoises were thread-trailed every day for a year in the Plaine des
Maures (Var) in order to estimate body index variation as it related to
movement, floristic association, water turnover rates (WTR) and field
metabolic rate. We collected data of two populations from
geographically distant sites possessing different degrees of habitat complexity
in France and in Greece (Hailey). In June, females moved 50 % more often
than males and travelled twice as far. Daily movement distances of Thh
in France range up to 408 m, but most were under 100 m. The movement distances
of males (mean 57 m) were shorter than those of females (mean 96 m). Home
ranges (HR) differed widely between the two areas, being four to five
times larger in France, but not between the sexes. We believe that HR
were larger in France because the habitat was more complex, and that greater
movements between vegetation types was advantageous for feeding and reproduction.
Nevertheless, after the summer dry period, we observed the opposite pattern.
Male movements were greater than females (mean daily distance moved in
July, males: 32.5m , females: 66.7 m and at the end of summer 75.8 and
32.2-50.6 m respectively. We also followed changes in WTR of Thh during
the year. During the spring 14 adults: mean WTR = 19.5 mL. kg-1.
d-1. There were no effect of sex and daily movement distances
on WTR, he tortoises were in water balance. During the summer: mean WTR
= 9.5 mL. kg-1. d-1. The mean WTR was only half
of that in spring suggesting that tortoises maintain a slightly negative
balance in summer. These results strongly suggest that the observed movement
distance do not affect WTR. In the French and Greek Thh populations, movement
patterns showed a strong interaction with habitat complexity during the
summer (in addition to sexual differences) as reflected by both the activity
levels and home range size. This study shows the importance of the consideration
of ecophysiological factors when setting to conservation strategies, and
the need for protected area size to be based on habitat complexity.
Carlos Arturo Navas
Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brasil
Altitudinal gradients in the tropical Andes are associated with decreased biological diversity and depauperate communities at extreme high elevations. Despite this overall tendency, some systematic groups are more affected than others by the extreme high-elevation climatic conditions. An interesting pattern, for instance, emerges when lizards and anurans, the most studied groups of high-elevation vertebrate ectotherms, are compared. Relative to lizards, anurans experience a significantly lower decrease in biodiversity at extreme high elevations; this is an intriguing difference as both groups share some common physiological traits. The data available, however, suggests that the thermal physiology of anurans tends to be more plastic. Reptiles thermoregulate behaviorally and can maintain similar activity temperatures along altitudinal gradients, but amphibians generally do not thermoregulate and compensate for differences in environmental temperature by means of physiological adjustments. This difference, together with a greatly reduced cost of maintenance in amphibians, seem partially responsible for the comparatively greater biodiversity of amphibians in high-elevation ecosystems.
Biodiversity: A Molecular Perspective
Kenneth B. Storey
Institute of Biochemistry, Carleton University, Ottawa, Canada K1S 5B6
kenneth_storey@carleton.ca
Recent advances in biochemistry and genetics are revolutionizing molecular techniques making them both much easier to use and much more comprehensive in their outcomes. The introduction of DNA arrays, for example, now makes it possible to scan for changes in the expression of thousands of genes whereas automated sequencing makes it easy to identify gene/protein variations that may contribute to biodiversity. Major advances in understanding the molecular components of various adaptive strategies (e.g. anoxia tolerance, freeze tolerance, hibernation) may also help us to understand why some species can radiate into harsh environments whereas others do not. For example, good dehydration tolerance and ischemia resistance appear to be integral to freeze tolerance and hence the pre-existence of these capabilities may contribute to the "choice" of winter hardiness strategy used by different species. Biochemical analysis also offers examples of basic metabolic pathways bent to new uses as well as the rapid evolution of novel protein types, both of which also impact on biodiversity. My talk will explore some of the molecular techniques and the metabolic issues that can contribute to unraveling issues of biodiversity.
Saguaro cacti and the species diversity of a desert bird community; an assessment of water and nutrient resource use with stable isotopes.
Blair O. Wolf and Carlos Martinez del Rio.
Department of Biology, The University of New Mexico, Albuquerque, NM
87131-1091, USA email -wolf@unm.edu;
Department of Zoology and Physiology, The University of Wyoming, Laramie,
WY 82071-3166, cmdelrio@uwyo.edu.
Resource availability and abundance importantly affect the diversity
and abundance of animals in many ecosystems. In hot subtropical deserts,
water and nutrient resources are commonly in short supply and their availability
for avian consumers may be limited by thermally imposed constraints on
foraging activity. In the Sonoran Desert of North America, the fruit of
large columnar cacti such as the saguaro, Carnegiea gigantea, are
probably the most abundant water resource during the hottest and driest
periods of the summer. Understanding the importance of the saguaro to
the water and nutrient balance of animal consumers can help us understand
how the saguaro's presence influences biodiversity in animal communities.
Stable isotope methods provide important insight into these plant -animal
interactions. The natural abundance of stale isotopes of carbon, nitrogen
and hydrogen in consumer tissues provide a direct link to the resources
consumers are exploiting. The saguaro, for example, has distinctive carbon
and hydrogen isotope values compared to other resources in the environment
that can be traced into consumer tissues. We used carbon isotope measurements
of avian tissues to describe the intensity of saguaro use by a desert
bird community. Hydrogen isotope measurements of the body water in avian
consumers provided information as to the importance of saguaro fruit as
a source of water. Nitrogen isotope ratios of consumer tissues potentially
enable the determination of the number of trophic levels that the saguaro's
resources have moved across before entering the consumer.
The mammal species gap: The locomotory limitations of flat feet
Barry G. Lovegrove1) and Linda Haines2)
1)School of Botany and Zoology, University of Natal, P/Bag X01 Scottsville,
South Africa
2) School of Mathematics, Statistics and Information Technology, University
of Natal P/Bag X01 Scottsville 3209, South Africa
Tel: 27-33-26-5113, Fax: 27-33-260515, email: lovegrove@nu.ac.za
Elucidating the mechanisms that determine the body sizes of mammals is crucial to understanding mammal evolution. We argue that the unimodal, right-skewed distribution most frequently identified in contemporary analyses obscures an underlying multimodal distribution associated with locomotory modes. We examined three assemblages (Afrotropical subregion, Australia and Nearctic) and log body masses follow multimodal distributions comprised of mixtures of normal distributions of plantigrade, digitigrade, unguligrade and saltatorial (hopping) mammals. In all three assemblages a species gap occurs at body sizes between 340 - 900g at the interface between the largest body masses of plantigrade mammals and the smallest body masses of digitigrade (Africa, Nearctic) or hopping mammals (Australia). The gap is associated with high rates of historical extinction (Australian fauna) and long-term evolutionary avoidance (Nearctic fossil record). We argue that interdependencies of predation pressure, locomotory limitations (plantigrade mammals) and resource reliability provide a reasonable explanation of the structure the distribution.
The pulmonary surfactant system: An evolutionary constant in a sea of structural diversity.
Christopher B. Daniels and Sandra Orgeig
Department of Environmental Biology, University of Adelaide, Adelaide, SA 5005, Australia
Pulmonary surfactant (PS), a mixture of phospholipids (PL), particularly disaturated PL (DSP), cholesterol (CHOL) and proteins reduce surface tension of the fluid lining the inner lung, thereby increasing lung compliance. Non-mammalian PS acts as an anti-adhesive, prevents alveolar edema, aids the muco-ciliary escalator and is anti-microbial/viral. These different roles require different surfactants, such that surface activity varies dramatically between species. The surfactant system has been highly conserved, morphologically and biochemically throughout (and despite) the enormous radiation of the airbreathing vertebrates. The lipid composition is conserved, and homology of the PS proteins SP-A, and SP-B demonstrates a single evolutionary origin for the system. The relative proportions of DSP and CHOL vary in response to lung structure and body temperature (Tb), but not phylogeny. The CHOL content is highest in saccular lungs, or species with low Tb. DSP/PL and DSP/CHOl is highest in complex lungs (bats) or species with high Tb. The CHOL content of PS increases in response to acute decreases in Tb in lizards, marsupials and bats to maintain fluidity of the lipids. The development of the surfactant system is similar in egg-laying and placental vertebrates, and is controlled by thyroid and adrenal hormones. Hormonal influences disappear after birth when adrenaline, acetylcholine and temperature control the system. Temperature modulates the release of surfactant from the type II cells by controlling the affinity of the receptors to neurotransmitters. The surfactant system is a neatly packaged system, located in a single cell and is highly conserved, yet spectacularly complex. The surfactant system is one of the best systems we know to examine evolutionary processes in physiology as well as gain important insights into gas transfer by complex organisms.
Supported by the Australian Research Council
Altered Dietary Selection in an Herbivorous Insect: the Effect of Parasitism
Richard A. Redak and S. Nelson Thompson
Department of Entomology, University of California, Riverside, CA 92521
(redak@citrus.ucr.edu)
We examined the influence of the Hymenopteran parasitoid, Cotesia
congregata, and dietary conditioning on the nutritional ecology of
the insect herbivore Manduca sexta. When parasitized, M. sexta
displayed altered food selection when given a choice of two artificial
diets, one high in protein vs. one high in carbohydrate. Unparasitized
larvae consumed the two diets in a ratio of approximately 2:1 protein
to carbohydrate while parasitized larvae shifted their consumption to
1:1 protein to carbohydrate. The shift in consumption was due to a reduction
in the amount of protein diet consumed and led to a reduction in growth
of the herbivore. Conditioning the herbivore on one or the other diets,
prior to parasitism, had little long-term effect on subsequent feeding;
however, both normal and parasitized larvae initially fed on the opposite
diet immediately after conditioning. It appears that the shift in diet
consumption due to parasitism may be advantageous for the parasitoid.
Parasitized M. sexta produced both the maximum number of parasites
and the maximum amount of parasite biomass when the larvae consumed a
diet consisting of 1:1 protein to carbohydrate. Varying from the 1:1 diet,
led to reduced parasitoid production. These results suggest altering food
intake in the host insect, may be adaptive for the parasitoid.