Don C. Forester

Sexual selection in the spring peeper, Hyla crucifer (Amphibia, Anura): role of the advertisement call

1. The advertisement call of the spring peeper exhibits significant variation in each of the four parameters examined: intensity, duration, frequency, repetition rate. 2. In playback experiments involving calls differing in a single parameter, females exhibited preference for loud calls, calls with a rapid repetition rate and low frequency calls. 3. Although we had hypothesized that females would prefer long calls to short calls, they did not. We attribute this lack of preference to unanticipated differences in the sound envelope of the two experimental calls. 4. Non-random choice by females during playback experiments may have been in response to the conspicuousness of the male call, or to encoded clues pertaining to male fitness. 5. Call repetition rate is positively correlated with body size (snout-vent length) while frequency is negatively correlated. 6. Anuran growth is thought to be indeterminate, so that larger males are typically older males. As a consequence of having survived longer, large males may be more fit. 7. Since females exhibited a preference for call parameters which were correlated with body size, we had anticipated that large males would experience differential mating success in nature. A comparison of amplexed and non-amplexed males over a three year period revealed no intergroup size difference. 8. We conclude that while females may select calls indicative of size, and perhaps fitness, during laboratory trials, such choices are likely more difficult in an active breeding congregation where acoustical interference and competition may tend to obscure call variation. 9. Finally we report the presence of small, non-calling satellite males and suggest that their success as sexual parasites may have influenced the size relationship between amplexed and non-amplexed males in our study.

PRIOR RESIDENCE EFFECT IN THE DART-POISON FROG, DENDROBATES PUMILIO

Each of 32 male, Dendrobates pumilio (red phase) were allowed to establish a territory in one half of a 40 liter aquarium. Each enclosure contained a substrate of Sphagnum, a potted plant, and a water dish. Males occupying the same aquarium were prevented from seeing one another by an opaque barrier. In the first experiment, residents were presented with a conspecific intruder matched for size and color. Based on a numerical index of aggression, residents were consistently dominant over intruders. When reciprocal trials were conducted, the results were reversed (i.e. residents were dominant over males to which they previously had been subordinate). The success of resident males was not influenced by the size of conspecific intruders. In addition, residents consistently dominated a sympatric confamilial intruder (Phyllobates lugubris). Removal experiments revealed that resident males recognize and defend their enclosures after 3, and to a lesser degree, 6 days of isolation. We also examined the effect of territorial markers on the prior residence effect by stepwise removal of the plant and Sphagnum. Residents aggressively defended enclosures in both experiments. When Sphagnum was removed from the residents enclosures and placed in a previously unused aquaria, 7 of 10 males exhibited dominance over conspecific intruders.

Significance of satellite males in a population of spring peepers (Hyla crucifer)

correspondence between genetic and morphologic variability patterns in Atlantic herring (Clupea harengus). Heredity 53:687-704. SHAKLEE, J. B., C. S. TAMARU AND R. S. WAPLES. 1982. Speciation and evolution of marine fishes studied by the electrophoretic analysis of proteins. Pac. Sci. 36:141-157. SKIBINSKI, D. O. F., AND R. D. WARD. 1982. Correlation between heterozygosity and evolutionary rate of proteins. Nature 298:490-492. SNEATH, P. H., AND R. R. SOKAL. 1973. Numerical taxonomy. Freeman and Co., San Francisco, California.

Post-Breeding Dispersal and Summer Home Range of Female American Toads (Bufo americanus)

Abstract While many amphibians have complex life cycles involving a primarily terrestrial adult phase and an aquatic larval phase, use of terrestrial habits by adult forms remains poorly understood. We used radiotelemetry to track the post-breeding dispersals of 16 female Bufo americanus during the summer and fall of 2001 to determine the extent of upland habitat use by females of this species. Female toads dispersed a minimum of 250 m and up to 1000 m from the breeding pond with the majority (97%) of relocations occurring more than 400 m from the breeding site. Typically dispersal paths were non-random and linear, punctuated by periods of sedentary behavior. During periods of sedentary behavior females confined their activities to an area of several m2. Females employed 24-h movements of up to several hundred m when moving between activity centers. For 8 toads with > 22 recaptures, total area of upland habitat utilization ranged from 434 to 1305 m2 (mean = 717.7 m2). All 16 toads were lost prior to entering winter torpor, including 10 confirmed cases of predation. Our study of post-breeding dispersal by female American Toads suggests terrestrial habitat use extending up to 1 km from the breeding site is common, and emphasizes the need for consideration of terrestrial as well as aquatic habitats in the development of conservation plans.

Age structure in a population of red-spotted newts from the allegheny Plateau of Maryland

The red-spotted newt, Notophthalmus viridescens, is widely distributed in North America east of a line stretching from southern Quebec to the upper Gulf Coast of Texas (Mecham, 1967; Conant, 1975). The species exhibits a complex life history which includes an aquatic larva, a terrestrial juvenile (eft), and an aquatic adult. The duration of these life history stages is variable. In upland populations, larvae characteristically hatch during the spring and summer and engage in post-larval migrations during the late summer and early fall (Hurlbert, 1970; Healy, 1975a; Gill, 1978a, b). Juveniles spend from 2-7 years as terrestrial efts before returning to the aquatic habitat to spend 1-9 years as mature, sexually active adults (Hurlbert, 1969; Pough, 1971; Healy, 1975b; Gill, 1978a, b, 1985). In coastal plain populations, the terrestrial eft phase is rare and in some localities may be omitted altogether (Noble, 1926, 1929; Healy, 1975a). In these populations, larvae metamorphose directly into adults and reach sexual maturity after two years. Historically, estimations pertaining to the age structure of various populations of the red-spotted newt have been based on one of two techniques: (1) a comparison of size-frequency histograms derived from sequential field collections; or (2) multi-year mark and recapture techniques. In the first technique, accuracy is influenced by variability in individual growth rate. The growth rate of newts comprising each of the life history stages is directly proportional to the amount of food consumed (Springer, 1909). Food consumption depends upon resource availability and the intensity and duration of individual activity. The activity of terrestrial efts is positively correlated with humidity and temperature (Healy, 1973), while that of aquatic juveniles and adults is inversely correlated with temperature (Springer, 1909). The use of a mark and recapture technique to estimate age structure maximizes accuracy, but requires a prolonged and often impractical time commitment (see Gill, 1985). In this report we apply the technique of skeletochronology to estimate the age structure and relative duration of the eft and adult life history stages of redspotted newts taken during a single sampling event. Seventy-six red-spotted newts (10 larvae, 36 efts and 30 adults) were collected from the Blue Ridge Physiographic Province of western Maryland (elevation 800 m) during June, 1984. The site consisted of a eutrophied farm pond surrounded by steep slopes covered by a second-growth, mixed mesophytic forest. Larvae and adults were collected from the shal-

GAUNTLET BEHAVIOUR AS A MALE SEXUAL TACTIC IN THE AMERICAN TOAD (AMPHIBIA: BUFONIDAE)

1. Toads comprising the Towson population are characterized by a prolonged breeding season (> 5 weeks), and some males remained at the site for at least 23 days. 2. During the breeding season, sexually active males may be classified as terrestrial or aquatic. 3. Although we did not observe males switching tactics during the same calling session, we recorded within and between season shifts. 4. On any given night, a few aquatic males engage in vocalization to attract females, while the majority actively swim about the pond surface attempting to intercept females or to displace males that have achieved amplexus. 5. Terrestrial males are smaller (on average) than pond males and are consistently positioned a few meters from the rim of the pond, facing the forest. 6. Terrestrial males intercept approximately 70% of the females approaching the pond, and 60% of these remain in amplexus after an hour, despite numerous displacement attempts by conspecific rivals. 7. Except for the first few nights of migratory activity, males achieving terrestrial amplexus are significantly smaller than would be expected by chance. 8. We hypothesize that male toads exploit a terrestrial tactic of mate capture if their advertisement call is relatively unattractive to females, and if they are too small to displace successful males from amplexus. 9. As males increase in size (with age), they move to the pond and switch to a mating tactic involving both vocalization and sexual parasitism. 10. In most instances, terrestrial males integrate visual, chemical and seismic cues to identify females.

Influences of wetland and landscape characteristics on the distribution of carpenter frogs

The distribution of wetland breeding amphibians may be influenced by multiple habitat variables interacting at various scales. We applied a multi-scaled modeling approach to relate the presence and absence of carpenter frogs (Lithobates virgatipes), a species of conservation concern in Maryland, to several wetland and landscape characteristics. We also investigated relationships between wetland habitat quality and adjacent landscape composition using correlation analysis and summarized those relationships in a hierarchical path model. Breeding call surveys were conducted at 40 wetland sites to determine the presence of calling male carpenter frogs. We collected data on aquatic and terrestrial habitat using both on-site measurements and geographic information system analyses. Logistic regression modeling revealed that wetlands occupied by carpenter frogs were significantly more acidic, exhibited intermediate hydroperiods, and had higher proportions of surrounding forest cover than did sites unoccupied by carpenter frogs. Path analysis revealed forest cover exhibited a negative correlation with wetland pH and hydroperiod. Our study corroborates a growing body of research that suggests the distributions of many amphibians are related to forest cover adjacent to wetland habitat and provides evidence on the importance of forest cover for maintaining wetland habitat quality.

Kin Recognition in a Brooding Salamander

Egg guarding, or ‘brooding’, by the mountain dusky salamander (Desmognathus ochrophaeus) is an example of maternal behaviour that can be experimentally manipulated and described quantitatively. It has been demonstrated that females of this species can specifically recognize, and will preferentially brood, their own eggs over those of a conspecific. We investigated whether this behaviour would extend to the selection of eggs of a more genetically similar animal in preference to those of a less similar animal, as might be predicted by inclusive fitness theory. We report here a highly significant correlation between time spent brooding and genetic similarity determined by random amplification of polymorphic DNA (RAPD) analysis. This is the first demonstration of a quantitative relation between genetic relatedness and maternal care in amphibians. Our findings have implications for the nature of maternal kin recognition in amphibians and its effect on kin selective behaviour in this class.

The Significance of Persistent Vocalisation By the Spring Peeper, Pseudacris Crucifer (Anura: Hylidae)

1. Male spring peepers exhibit individual variation in calling persistence within as well as between nights. 2. Weather conditions influence nightly variation in calling persistence throughout the reproductive season, but there is a pronounced decrease in calling persistence late in the season which appears to be independent of climate. 3. In four speaker experiments simulating males calling 20, 40, 60, and 80% of the time, there is a positive correlation between time spent calling and mating success. 4. On nights when there is significant variation in calling persistence, females likely respond to those males which are most persistent (i.e. , produce the most conspicuous calls). 5. In four speaker experiments simulating males calling 80, 85, 90 and 95% of the time, mating success is random, suggesting that during periods of peak mating activity the importance of female choice is diminished. 6. Calling persistence is not correlated with body size, therefore males of any age or size class have an opportunity to experience mating success. 7. Anuran vocalization is known to be energetically expensive, and persistent callers (regardless of their size) are likely in good physical condition. 8. We suggest that by responding (either actively or passively) to the most conspicuous calls, females convey to their offspring an advantage above and beyond that accrued by random mating.

The Significance of Antiphonal Vocalisation By the Spring Peeper, Pseudacris Crucifer (Amphibia, Anura)

1. Male spring peepers respond to acoustic interference from an encroaching conspecific with a graded behavioral sequence: they increase their call repetition rate, they emit one or more encounter calls, they entrain their calls to those of the intruder. 2. Once entrained, males continue to call synchronously for extended periods. 3. The time interval between the end of the leaders call and the beginning of the followers call (the intraduet interval) is consistent, and is maintained despite changes in the duration or repetition rate of the leaders call. 4. Our data corroborate earlier investigators who concluded that the follower is stimulated by the onset of the leaders call, but is inhibited from calling until a fixed time interval after the leader has ceased calling. 5. Controlled discrimination tests reveal no differential mating success by the leader or the follower within a simulated duet. 6. Females exhibited a significant preference for a duet over a soloing male. 7. Although test females were able distinguish between the simultaneous broadcast of two phase-locked call sequences differing only in frequency, they did so in the absence of alternative, uncovered calls. 8. We conclude that antiphonal vocalisation functions primarily to reduce the potential for broadcast interference during the initial phase of female phonotaxis.