Mass-specific Growth Research Articles

Growth Plasticity and Thermal Opportunity in Sceloporus Lizards

We studied the relationship between daily active time and growth rate in hatchling sagebrush lizards (Sceloporus graciosus), a mainly montane species, and western fence lizards (Sceloporus occidentalis), which inhabit a broader range of thermal environments. The study involved two populations of each species along in altitudinal gradient in southern California and one population of S. occidentalis from Oregon. In the field daily activity time varied seasonally: activity periods were short during spring and fall and longer during the summer. Activity patterns also varied geographically: in montane and high latitude environments, hatchlings experienced reduced opportunity for growth both daily and seasonally, because fewer, shorter days are available before the end of the activity season. We conducted laboratory experiments to measure the effect of the thermal environment on hatching growth rates. Laboratory—incubated hatchlings had access to radiant energy for part of each day and were kept at 15°C (too low for activity) the rest of the day. The four experimental treatments (6, 9, 12 and 15 h of radiant energy per day) approximated the range of thermal environments encountered by hatchlings in the wild. Food and water were provided ad libitum. Mass—specific growth rates were plastic and generally increased with potential activity time in hatchlings from all populations. However, the form of this relationship varied among populations: growth rates of California S. occidentalis (growth opportunities) increased roughly linearly with potential activity time, whereas growth rates of Oregon S. occidentalis and California S. gracious (short—day specialists) showed curvilinear responses to potential activity time. Interspecific and large—scale intraspecific differences in the form of the norm of reaction paralleled the differences in thermal environments encountered by hatchlings in nature. Populations of S. occidentalis at low elevation in California routinely experience short and long days of activity (e.g., 6—13 h/d) and the norm of reaction for growth rate increases linearly over this range. In contrast, populations of S. graciosus rarely experience days with >9 h of activity and the norm of reaction for growth rate plateaus above 9 h/d. Similarly, northern populations of S. occidentalis from Oregon rarely experience days with >9 h of activity and the norm of reaction for growth rate also plateaus above 9 h/d. On a large scale, therefore, growth responses appear to be appropriate to the thermal environments to which hatchlings are most commonly exposed. However, conspecific populations from different altitudes in California did not differ in growth response, although hatchlings experience different thermal environments in nature. We observed substantial among—family variation in growth rates of S. occidentalis, which may indicate genetic variation, a prerequisite for evolution by natural selection. Moreover, significant family x treatment interaction effects on growth rate that reflect underlying genotype x environment interactions indicate a genetic basis to the observed intraspecific and interspecific differentiation in the norm of reaction. Additional experiments demonstrated that (1) reducing food availability by 50% reduced growth rates by 50% in both species, and (2) growth rates did not differ between hatchlings whose eggs were incubated at 24° vs. 27°C.

Comparative Growth and Survival of Dreissena polymorpha and Dreissena bugensis, Exotic Molluscs Introduced to the Great Lakes

Zebra ( Dreissena polymorpha) and quagga mussels ( D. bugensis) are among the most recent species to invade the Great Lakes. This study explored growth rates of two size classes (5 and 15 mm) of each species reciprocally transplanted into western and eastern Lake Erie, and in laboratory experiments in which environmental temperature and food concentration were varied. Both species and size classes experienced high survival rates in western (>95%) and eastern (> 85%) Lake Erie. Length-and mass-specific growth rates varied significantly between locations and mussel size classes, but not by species. Mussels incubated in the warm, western basin of Lake Erie exibited growth {length and mass), whereas those in the cooler eastern basin did not. In a laboratory experiment, temperature and size were the most important determinants of growth, though species differences were evident. Growth of both species was greater at 15°C than at 6°C. Specific growth rates of zebra mussels were greater than those of quagga mussels, except with respect to mass growth of smaller mussels at the higher temperature. Large mussels of both species experienced no mortality, whereas small quagga mussels experienced a significantly higher rate of mortality (50%) at the higher temperature than did small zebra mussels (10%). Results of the present study indicate that mussel growth of both species corresponds with initial size and environmental temperature, and that the distribution of quagga mussels in the Great Lakes is unlikely to be determined by high water temperature.

Growth, production and ecological significance of Ophiura albida and O. ophiura (Echinodermata: Ophiuroidea) in the German Bight

Growth and production of the shallow-water ophiuroids Ophiura albida and O. ophiura were investigated at two stations in the German Bight from 1988 to 1991. Growth rings visible on the vertebral ossicles of the ophiuroid arms were interpreted as annual age markers. A correction for overgrown first rings allows for more exact estimations of growth and age. In both species growth could be described by Von Bertalanffy growth functions with the asymptotic disc diameter D ∞=10.1 mm, K=0.229 and t o=-0.192 in O. albida and D ∞=27.7 mm, K=0.084 and t o=0.042 in O. ophiura. Somatic production was calculated from mass specific growth rates. Annual production:biomass (P:B) ratios were estimated at 0.32 for O. albida and 0.43 for O. ophiura.

Allocation of Matter in the Body of Growing Toads, Bufo bufo: Components of ‘Condition’

AbstractThe condition, CI = [body mass (g)/length (cm)3]‐1000, tends to increase in toads growing in the laboratory on a diet of meal‐worms. The allocation was therefore studied of ingested food to growth corresponding to maintenance of standard condition (ΔWS) and to increases in condition, expressing bulky growth. A condition index of 100, typical of toad populations, is chosen to characterize standard growth, higher values expressing bulky growth. The relationship between mass specific standard growth (ΔWs/W0) and actual growth in mass (ΔW/W0) was the same in controls and growth hormone‐treated toads and was independent of sex and season. It could be described by the allometric equation ΔWs/W0 = 0.28 (ΔW/W0)1.36, r = 0.93. The composition of mass representing increases in bulk in excess of a CI = 100 was assessed from allometric relationships established between the indices of the chemical constituents and the overall condition index. The increases in condition were partitioned among the organs and parts of the body from allometric relationships established between indices of organs and body parts and the overall condition index. Treatment with growth hormone enhanced growth in mass and significantly increased the relative proportion of mass allocated to standard growth. However, the effect was not specific to growth hormone, but was an indirect effect of the increased growth rate. Water was the predominant constituent of the growth in bulk, amounting to about 70% of increases in CI. Fat and protein contributed about equally initially, 5–10%, with fat strongly increasing and protein slightly decreasing with increasing condition, fat to approach 20–30% when CI approached 200. Increases in water content largely reflected increases in volume of blood and lymph.

Water Content, Thermogenesis, and Growth Rate of Skeletal Muscles in the European Starling

-We examined the relationship between function, water content, and growth rate of skeletal muscles in the European Starling (Sturnus vulgaris). Function was measured as the ability of nestlings to increase their rate of oxygen consumption in response to cold stress. Water content and growth rate of pectoral and leg muscles were determined for tissues dissected from a series of known-age nestlings. The maximum metabolic response to cold stress increased from 0 at 4 days of age to 4.5-5.5 cm3 O2g'-'h-' at 15-16 days. During this period, the mass of the leg muscles increased 5-fold and that of the pectoral muscles, 12.5fold. The water fraction (WF) of the pectoral muscles decreased from about 0.86 to 0.72, while that of the leg muscles decreased from 0.83 to 0.72. Of the variatlon in metabolic response to cold stress per gram of muscle, 89% could be related to the WF of skeletal muscle by a linear relationship. Over the ages surveyed, the metabolic response varied from 0 at WF = 0.85 to an increase above resting metabolism amounting to 60 cm3 02 gram of pectoral and leg muscle-' h-' at WF = 0.72. Also during this period, the growth rate of both muscle masses decreased with age and proportion of water, from a mass-specific growth rate of 0.5/day at WF = 0.85 to near 0 at WF = 0.72. If these relationships represent a balance between growth rate and functional maturity in developing tissues, then even small changes in function, associated with a change in water content of only a few percent, could have large consequences for the growth rate of the individual. Received 30 August 1983, accepted 30 November 1984. IN comparisons among species of birds of the same size, the growth rate of chicks varies over an approximately 10-fold range (Ricklefs 1979b). Much of this variation is associated with the mode of development. Chicks of precocial species, which are relatively independent of their parents from an early age, grow more slowly than do those of altricial species, which depend upon their parents for food and warmth during much of their development. Such comparisons, and the observation that mass-specific growth rates of individuals slow as the individual matures functionally, led Ricklefs (1969, 1973, 1979a) to suggest that growth rate is inversely related to functional maturity at the tissue level. As a tissue differentiates and begins to function at an adult level, its proliferation by cell division and growth by cell enlargement decrease. Skeletal muscle provides a model for this constraint in that as mesenchyme cells (myoblasts) of the embryonic muscles differentiate, they fuse to form muscle fiI Present address: Department of Zoology, University of Washington, Seattle, Washington 98195 USA. bers and cease to proliferate (Holtzer 1970, Cameron and Jeter 1971). Associated with the maturation of tissues is a decrease in content of water (Ricklefs 1967, 1979a; Bilby and Widdowson 1971; O'Connor 1977; Dunn and Brisbin 1980). In comparisons among species and in comparisons among individuals during development, the water content of a tissue has frequently been used as an index to its differentiation and functional maturity. But in spite of the general association between water content, function, and growth rate, these relationships have not been determined quantitatively. Indeed, Marsh and Wickler (1982) have questioned the use of water content as a suitable index of muscle function. We examined the relationship between function, water content, and growth rate of skeletal muscles in the European Starling (Sturnus vulgaris). Skeletal muscle was chosen for two reasons: first, its pattern of development has been suggested to underlie differences in growth rate (1/time) among species of birds (Ricklefs 1979a, b); second, the function of skeletal muscle can be determined directly by simple physiological measurement. During development, increase in 369 The Auk 102: 369-376. April 1985 This content downloaded from 157.55.39.25 on Tue, 02 Aug 2016 06:21:48 UTC All use subject to http://about.jstor.org/terms 370 RICKLEFS AND WEBB [Auk, Vol. 102