Abstract

To assess the possibility of thermal effects on reproductive function as a range-limiting mechanism in cottonmouths, we investigated the effects of temperature/photoperiod regimes on monthly male testosterone levels in three groups. The first was a field group, the second was a lab control group that received natural temperature/photoperiod conditions, and the third was an experimental lab group that received temperature/photoperiod conditions of a region north of the current range limit. The field and lab control groups exhibited a single testosterone peak in August (34.4 and 14.1 ng ml⁻¹, respectively) that coincided with observed reproductive activities in Northwestern Arkansas. The experimental group also exhibited a single peak (11.7 ng ml⁻¹), but the peak was delayed by one month. We coupled energetic calculations with environmental temperature, the timing of reproductive events, and the time available for foraging to demonstrate how pre- and postcopulation reproductive failure may serve as a sublethal range-limiting mechanism. North of their current range limit, the reduced time for energy acquisition may not allow for sufficient juvenile recruitment into the population to replace losses. Therefore, cottonmouths may be prevented from establishing a more northern range limit due to their reproductive physiology.

Abstract

To assess the ways in which different selection pressures on male and female spinyhead blennies (Acanthemblemaria spinosa) influence their use of space, we measured a number of features of their shelter sites. Both sexes occurred primarily on dead surfaces of elkhorn coral (Acropora palmata), but significantly more males than females were found on live coral surfaces. Males occurred twice as frequently as females in the vacated constructed tubes of serpulid worms or vermetid molluscs, which provide greater surface for egg deposition than the shorter cavities excavated by other organisms. There was no difference between the sexes in shelter height above the reef surface. Fish size was positively correlated with shelter height above the reef surface for both sexes. Number of eggs being guarded by males was positively correlated with both fish size and shelter height above the reef surface; in concert they account for 44% of the variance in egg number. To assess the effects of competition, we removed spinyheads from corals and documented recolonization along with shelter site parameters. Corals originally harboring larger fish were recolonized at a higher rate, and in all cases the mean size of recolonists was smaller than originals; the original correlation of fish size with height above the reef surface collapsed for recolonists. These observations are consistent with others that indicate that spinyhead blennies compete for quality shelters.

Abstract

We examined the energetics of calling by male Crinia georgiana because other studies have shown that the costs of attracting a mate for male frogs can limit chorus participation, which in turn can explain significant variation in male mating success. The metabolic cost of producing a single note for C. georgiana (0.0006 ± 0.0001 ml O₂ g⁻¹ min movement⁻¹ note⁻¹) was similar to the cost for other species, but males called at a comparatively low rate (mean = 136.0 ± 21.5 calls per hour). The production of multiple-note calls by C. georgiana is not an energy-saving mechanism because it is not more expensive to produce the same number of notes with single-note calls. Most males were found at the breeding site on one or two nights only during the breeding season, and peak calling activity occurred for approximately nine hours per day. Further, there were only two nights of peak chorus activity during the breeding season (82 days). These data suggest that the overall reproductive effort of male C. georgiana is low. We also show that female mate choice preferences for call rate might allow males to call at a low rate. We discuss the possibility that a positive relationship between male mating success and chorus attendance may not hold for all males in a species because the costs and benefits of attending the chorus can vary considerably among individuals.

THE ROCKFISHES OF THE NORTHEAST PACIFIC. Milton S. Love, Mary Yoklavich, and Lyman Thorsteinson. 2002. University of California Press, Berkeley, California. ISBN 0-520-23437-5 (cloth), 0-520-23438-3 (paper). 414 p. $60 (cloth), $24.95 (paper).—The stated reason for writing this book is that “rockfishes are cool … very cool.” So is this book. I've never seen anything quite like it. It is a cornucopia of things rockfish—from art to history to humor to personal experience to science. Ray Troll's ROCK cover (look for the guitar) is a visual teaser for the lavish interior's 550 color photographs, 220 black-and-white illustrations, and 75 maps.

The

Apareiodon Eigenmann, 1916 (Teleostei, Characiformes), from the Tocantins-Araguaia Basin, with Description of Three New Species