Neil F. Hadley

Lizard reproductive effort: caloric estimates and comments on its evolution

The energy content of eggs of 10 lizard species was determined and used as a measure of reproductive effort (ratio of clutch calories to body calories). Values for eggs ranged from 5.87 to 7.20 cal/mg ash-free dry weight (x = 6.37). Species differences in calories going into reproduction during a breeding season, however, were primarily due to differences in clutch size and clutch frequency between species. Correlation analysis between three mea- sures of reproductive effort, including the preceding, and a suite of demographic variables revealed only one significant correlation (negative) between clutch calories to body calories ratio and mean annual adult survivorship. The energy allocated to eggs in comparison to total annual energy expenditure was estimated for three of the species investigated. Sceloporus graciosus had the highest reproductive effort, with proportional values for first and older breeders about the same. The proportion of total energy expended on reproduction was slightly lower for Uta stansburiana, with first and older breeders exhibiting the same effort. Scelop- orus jarrovi had the lowest reproductive effort, but showed an increasing effort with increasing age. These data suggest that the demographic environment may not be the primary selec- tive pressure determining reproductive effort, and that reproductive effort may not be posi- tively correlated with age in all species.

Epicuticular lipids of the desert tenebrionid beetle, Eleodes armata: Seasonal and acclimatory effects on composition

Abstract The chemical composition of the epicuticular lipids of the desert tenebrionid beetle, Eleodes armata , was analyzed by thin layer and gas chromatography. Total lipid extracted from beetles sampled throughout the year ranged from 0.10 to 0.28% of their fresh wt. Hydrocarbons were most abundant (70 to 90+ %); alcohols, sterols, free fatty acids, and triglycerides were also detected. Hydrocarbons were comprised of over 25 components, all saturated, containing 26 to 44 carbon atoms. Branched alkanes accounted for 92.3% of the total hydrocarbons and were responsible for all components having chain lengths greater than 34 carbon atoms. Fractional equivalent chain lengths indicated the presence of internally branched monomethylalkanes and 3-methylalkanes. n- Alkanes accounted for only 7.7% of the total hydrocarbon fraction; they consisted of even- and odd-numbered chains containing 27 to 34 carbon atoms. Summer beetles, and winter beetles acclimated to 35°C for periods of 5 and 10 weeks exhibited higher quantities of hydrocarbons and a higher percentage of long chain components than did winter beetles or appropriate controls. Dietary (lettuce) n- alkanes had little effect on beetle epicuticular hydrocarbon composition. The quantity, chain length, and degree of branching of the hydrocarbons are discussed relative to measured cuticular permeability of E. armata as well as compared to compositional/permeability relationships established for plasma and artificial membranes.

Cuticular Permeability and Epicuticular Lipid Composition in Two Arizona Vejovid Scorpions

Cuticular permeabilities in two Arizona vejovid scorpions reflect the temperature/relative humidity regimes of the habitats in which they were collected. Four lipid classes are present in significant proportions in the epicuticular lipids of both species: hydrocarbons, free fatty acids, cholesterol, and aliphatic alcohols. Surface densities of total lipids and hydrocarbons are inversely correlated with cuticular permeability. Epicuticular lipids of the more xeric-adapted species are characterized by higher proportions of long-chain branched hydrocarbons and long-chain saturated free fatty acids. The results indicate that cuticular permeabilities can be altered to meet environmental requirements, and that in scorpions predictable changes in epicuticular lipid composition are in part responsible.

Cuticular permeability of desert tenebrionid beetles: Correlations with epicuticular hydrocarbon composition

Cuticular transpiration and transition temperatures of four desert tenebrionid beetles (Eleodes armata, Cryptoglossa verrucosa, Centrioptera muricata, C. variolosa) were correlated with the quantity and chemical nature of their respective epicuticular lipids. A fifth species, Pelecyphorus adversus, had only its epicuticular lipids analyzed. Cuticular transpiration increased linearly between 25 and 40°C, but remained low for the beetles as a group in comparison to arthropods of moist habitats. Hydrocarbons comprised over 90% of the total lipids in each species; alcohols, free fatty acids, triglycerides, and cholesterol were also extracted. Hydrocarbons were completely saturated with odd-numbered chains containing from 25 to 33 carbon atoms predominating. The percentage of straight-chain (n-alkane) hydrocarbons ranged from 78.5% in C. verrucosa to only 7.7% in E. armata. The effective barrier to cuticular water flux in these beetles appears largely attributable to the presence of surface hydrocarbons. The least permeable species, C. verrucosa, was further characterized by having predominately long-chain, saturated n-alkanes. An even greater percentage of long-chain hydrocarbon molecules was found in E. armata; however, their effectiveness in reducing cuticular transpiration was possibly negated by an abundance of branched components. The potential for using hydrocarbon composition as a taxonomic tool for separating these species as well as predicting cuticular permeability is also discussed.

Micrometeorology and Energy Exchange in Two Desert Arthropods

Incoming solar, net, and reflected radiation, wind velocity, relative humidity, and temperatures at various levels above and below an open desert surface were recorded simultaneously at 30—minute intervals for a 3—day period. Concurrent measurements were also made of arthropod burrow temperatures and relative humidities, scorpion body temperatures, and body and subelytral temperatures of tenebrionid beetles. The burrowing habit enabled arthropods to escape the hot, desiccating conditions recorded on the desert surface during the day. Temperatures and humidities to which scorpions were subjected while in their subterranean retreats depended upon the burrows depth and subsequent movements in the burrow. Vertical movements between the surface and maximum burrow depths during a 24—hour period provided arthropods with a wide choice of micro— environments. Tenebrionid beetles on the surface were able to achieve a temperature equilibrium only under low temperature and radiation loads. Subelytral cavity temperatures in black Eleodes armata were generally 2—7°C warmer than body temperatures after exposure to direct sunlight. Temperature differences between subelytral cavities of black beetles and beetles with their elytra painted white were small, but suggested that a white dorsal surface was, at least, paritally effective in reducing absorption of solar radiation. The subelytral cavity, in addition to reducing transpiratory water loss, apparently provides a mechanism for increasing convective cooling, and may serve as a temperature “buffer zone” against heat conduction resulting from high intensity solar radiation. A heat exchange budget was estimated for E. armata on the desrt surface. Major contributing factors were heat gained from incoming radiation versus heat lost from convection and reradiation. Contributions from evaporation and metabolism, as determined by laboratory experiments, were very small in comparison, while the role of conduction in energy exchange was assumed to be negligible. Inherent problems in the estimation of contributing factors to net energy exchange, and comparison of similar budgets for mesic arthropods are discussed.

The effects of temperature and humidity on water loss in two desert tenebrionid beetles, Eleodes armata and Cryptoglossa verrucosa

Abstract 1. 1. Eleodes armata exhibited greater water loss than Cryptoglossa verrucosa at all temperatures and humidities. 2. 2. At low temperatures and humidities, water lost through transpiration predomated; at higher temperatures and humidities, a greater percentage was lost via quinone secretions. 3. 3. No uptake of atmospheric moisture was observed for either species, C. verrucosa exhibited a reduction in water loss with increased dehydration. 4. 4. The presence of intact elytra reduced water loss in E. armata . 5. 5. Resistance to desiccation in the two species was correlated with observations of their seasonal abundance and activities.

Ventilatory Patterns and Respiratory Transpiration in Adult Terrestrial Insects

Although respiratory surfaces constitute a potential site for dehydration in terrestrial insects, only afew studies have addressed the problem of respiratory transpiration in a manner that explicitly separates water loss associated with gas exchange from cuticular and other avenues of water loss. The most promising of these studies are recent investigations conducted on adult insects that release CO₂ intermittently (discontinuous ventilation [DV] cycle). Using either gravimetric techniques or electronic sensors to compare water lost during interburst (spiracles closed or fluttering, cuticular transpiration only) and burst (spiracles open, cuticular and respiratory transpiration) phases of the cycle, investigators have shown that respiratory water loss accounts for only a small percentage (1.9%-13%) of the total water loss at low to moderate temperatures (15° -30° C). The relatively low amount of water lost during the burst phase in lubber grasshoppers as well the timing and duration of discontinuous CO₂ release raises serious questions regarding the presumed water-saving function of the DV cycle.

Surface Activities of Some North American Scorpions in Relation to Feeding

Field and laboratory studies were conducted on the nocturnal surface activities any feeding behavior of scorpions, using ultraviolet light. Two species, Vejovis confusus and V. mesaensis, showed a decrease in surface occurrence as the evening progressed, while Centruroides sculpturatus showed a random occupation throughout the night. Increased intensity of moonlight resulted in a significant decrease in surface occurrence in V. confuses and V. mesaensis; C. sculpturatus showed no significant response to increased illumination. Species differences in the amount of surface activity and feeding behavior were noted. Potential prey, food preferences, and mechanisms used in prey detection are also discussed. See full-text article at JSTOR

Water loss in three species of tiger beetles (Cicindela): Correlations with epicuticular hydrocarbons

Abstract Water loss rates in dry air at 30°C and cuticular lipid/hydrocarbon composition were determined for three species (eight populations) of tiger beetles (Cicindela oregona, C. tranquebarica and C. obsoleta). The highest water loss rates were found in C. oregona (0.049 to 0.052 mg cm−2h−1 mmHg−1), a species active in spring and fall along water courses in Arizona, while the lowest rates were exhibited by C. obsoleta (0.022 to 0.028 mg cm−2h−1 mmHg−1), a summer-active species that inhabits dry grasslands. Water loss rates for C. tranquebarica were closer to those of C. obsoleta even though C. tranquebarica often coexists with C. oregona. Hydrocarbons were an important constituent of the cuticular lipids of all three species; smaller quantities of wax and cholesterol esters, triacylglycerols, free fatty acids, alcohols, and cholesterol were also detected. C. obsoleta contained the greatest amount of hydrocarbon per surface area. All of its hydrocarbon molecules were saturated, with branched components accounting for about 60% of the total fraction. Saturated (primarily n-alkanes) and unsaturated (n-alkenes) molecules were present in both C. oregona, which contained the lowest hydrocarbon surface density, and C. tranquebarica. The hydrocarbon composition of the three species is discussed in terms of its contribution to the epicuticular waterproofing barrier and its potential use as a chemotaxonomic tool.

Seasonal effects on cuticular permeability and epicuticular lipid composition inCentruroides sculpturatus ewing 1928 (Scorpiones: Buthidae)

SummaryThe epicuticular lipids of the scorpion,Centruroides sculpturatus (Buthidae), are composed mostly of hydrocarbons and cholesterol, with free fatty acids and alcohols being present in smaller proportions. Hydrocarbons of summer scorpions are predominantly long-chain branched alkanes. The fatty acid component is composed primarily of saturated and unsaturated sixteen- and eighteen-carbon molecules, while the aliphatic alcohols are primarily evenchain length molecules containing 18–32 carbon atoms. Hydrocarbons of scorpions collected during fall, winter and early spring are characterized by higher proportions of shorter n-alkanes, especially n-heptacosane and n-nonacosane. Transcuticular water loss rates of freshly-killed, sealed scorpions and total water loss rates of live scorpions are significantly higher in specimens collected in winter than in scorpions collected during summer months. The functional relationship between seasonal changes in cuticular permeability and epicuticular lipid composition is discussed.