Thomas A. Jenssen

Sexual Dimorphisms in Aggressive Signal Structure and Use by a Polygynous Lizard, Anolis carolinensis

Abstract Unlike many polygynous species, we found that females of the lizard, Anolis carolinensis, have the same repertoire of aggressive signals as males. These shared signals included three stereotyped headbob display patterns (types A, B, and C) that were performed with no significant intersexual difference in amplitude displacement. However, we did find the following sexual dimorphisms in signal structure and use. Females (1) had a smaller average extendable throat fan (i.e., dewlap) area (0.22 cm2) than males (1.52 cm2), (2) never displayed when alone (0/h), whereas males frequently did (18/h), (3) displayed 10-fold less during consexual encounters (17/h) than males (168/h), (4) lacked the ritualized intermale combat scheme of circling, jaw-sparring, and jaw-locking, (5) infrequently used physical contact in consexual encounters, whereas males frequently did, and (6) did not employ a shifting use of signals with decreasing interfemale approach distance, whereas contesting males did by decreasing the frequency of C displays in favor of A and B displays, decreasing the use of the dewlap during displays, and decreasing the sequencing of displays in volleys. These results are in accord with field studies, which report limited interfemale territoriality (i.e., low consexual threat) and short display broadcast distances, whereas male territorial behavior is well developed (i.e., high consexual threat), with frequent long-distance displaying between consexuals. We suggest that these displays, which function in competitive interference, have been less directionally selected in females than in males because the outcomes of consexual contests carry fewer reproductive consequences for females than for males.

Developmental effects of testosterone on behavior in male and female green anoles (Anolis carolinensis).

This study addressed the role of testosterone (T) in the development of sexually dimorphic behavior in the green anole lizard, Anolis carolinensis. We documented the pattern of endogenous T concentrations during ontogeny and we determined the behavioral effects of experimentally elevated T in juvenile males and females. T concentrations were measured in the plasma of hatchlings from eggs incubated in the laboratory, in juveniles of all sizes sampled in the field, and in the yolks of freshly laid eggs in the laboratory and were compared to plasma T in adult females (measured in this study) and adult males. There were no sex differences in plasma T in hatchling and small juvenile (<26-mm snout-vent length, SVL; <14 days old) males and females, concentrations of which in both sexes tended to decline over the 14-day posthatching period. Plasma T sharply increased in juvenile males, but not females, after approximately 14 days posthatching (>25-mm SVL), and it became significantly higher after approximately 38 days posthatching (>30-mm SVL). Plasma T for juvenile males was within the range detected in breeding adult females, but it was 20- to 45-fold lower than that of adult males, breeding or postbreeding. All eggs contained detectable yolk T, but eggs that gave rise to males contained nearly twice as much yolk T as those that gave rise to females. We do not know whether this yolk T comes from the mother, embryo, or both. In behavior trials conducted in the laboratory, juveniles (36- to 42-mm SVL) with T implants, regardless of whether they were male or female, had increased activity levels compared to juveniles with blank implants, due to increased rates of nearly every behavior monitored. These results are discussed in the context of the organization-activation theory of sexual differentiation and the particular life history of A. carolinensis.

Assessment in contests of male lizards (Anolis carolinensis) : how should smaller males respond when size matters?

Within a female-defence polygynous mating system, males of the lizard A. carolinensis use an array of stereotyped signals and aggressive tactics to acquire and defend long-term territories containing multiple, sedentary females. In competition, body size appears to be important because size of free-ranging males correlates positively with volume of male territories and number of patrolled females. Therefore, an ability to assess body size during territorial contests should be an adaptive attribute that would influence the tactics of intermale aggression. To examine this premise, we staged contests between 10 pairs of males matched for size (i.e. symmetric contests) and 10 pairs mismatched for size (i.e. asymmetric contests), while all 20 pairs of males were matched for habitat resources, a mate, and resident status. Overall, we found (1) contest profiles best fit the features of a ‘fixed-phase, sequential assessment’ model of game theory, (2) body size and mass were highly correlated with contest outcome, (3) none of 12 signal variables predicted contest outcome, and (4) paired males generally matched aggressive tactics and signalling behaviours. We also examined the asymmetric contest profiles for deviations from the profiles of symmetric contests. We tested the proposition that smaller males of size-mismatched contests would assess their disadvantage and choose a bluff strategy to mitigate risky behaviour and avoid fighting. We found, however, that the risk-mitigation hypotheses were unsupported. Smaller males were not playing a bluff strategy, but rather a hawk strategy. They initiated risky tactics by (1) invading the habitats of their larger opponents, an act that invited retaliation, (2) showing no tendency to stay away from larger opponents, (3) maintaining high levels of aggressive signalling as encounters intensified, and (4) engaging larger opponents in physical fighting, despite losing 90% of their encounters. These empirical results support a recent game theoretical construct (‘Napoleon complex’) that models size-asymmetric contests in which smaller males initiate fights that they usually lose. Our data suggest that, if smaller males of A. carolinensis have breeding territories, then they will engage in costly contests, despite a low probability of defeating larger and equally motivated opponents.

Size-Related Variation in the Advertisement Call of Rana clamitans (Anura: Ranidae), and Its Effect on Conspecific Males

VITT, L. J. 1981. Lizard reproduction: habitat specificity and constraints on relative clutch mass. Amer. Natur. 217:506-514. -, AND T. E. LACHER, JR. 1981. Behavior, reproduction, habitat and diet of the iguanid lizard Polychrus acutirostris in the caatinga of northeastern Brazil. Herpetologica 37:53-63. , R. C. VAN LOBEN SELS AND R. D. OHMART. 1978. Lizard reproduction: annual variation and environmental correlates in the iguanid lizard Urosaurus graciosus. Herpetologica 34:241-253. SAVANNAH RIVER ECOLOGY LABORATORY, DRAWER E, AIKEN, SOUTH CAROLINA 29801 AND BIOLOGY DEPARTMENT, WHITTIER COLLEGE, WHITTIER, CALIFORNIA 90608. CURRENT ADDRESS (LJV): BIOLOGY DEPARTMENT, UNIVERSITY OF CALIFORNIA, Los ANGELES, CALIFORNIA 90024.

Male mate choice by the lizard Anolis carolinensis: a preference for novel females

Laboratory and field manipulations tested whether male Anolis carolinensis lizards and discriminate preference for novel females over resident females. In 16 laboratory trials, we videotaped social interactions between paired males and females during baseline session (male and resident female housed together 1–3 weeks), resident-female session (male and reintroduced resident female), and novel-female session (male and novel female with resident female removed). We examined 22 behavioural variables. Male behaviours did not differ significantly between baseline and resident-female sessions, nor did female behaviours differ significantly between baseline, resident-female and novel-female sessions. However, between resident-female and novel-female sessions, males significantly increased display rate (320%), volleys of repetitive displaying (300%) and volley length (150%), and significantly decreased the distance (375%) and number (430%) of movements travelled away from the female. We concluded that males discriminate novel females from resident females independently of female behavioural or chemical cues. In each of 18 field trials, we first videotaped baseline social interactions of the resident male and females in a naturally occurring, polygynous, breeding group. The next day, we released two novel females into the territory (so at least one female remained) and videotaped subsequent social interactions. In comparison to baseline observations, males significantly increased the proportion of time spent in female-directed activities (from 5% towards resident females to 53% towards the novel female) and the proportion of displays directed towards novel females (from 6% towards resident females to 51% towards the novel female), and significantly decreased the proportion of time spent in territorial activities (from 75% to 19%) and the proportion of displays used in territorial activities (from 94% to 44%). Data from both experiments indicate that males appear to distinguish among individual females, and use this ability to increase reproductive success by identifying and preferentially pursuing novel females over previously inseminated resident females. From the perspective of cognitive ethology, we suggest a model by which males control mating decisions within their territories.

HETEROSEXUAL SIGNALLING BY THE LIZARD ANOLIS CAROLINENSIS, WITH INTERSEXUAL COMPARISONS ACROSS CONTEXTS

Summary We quantie ed the structure and use of signals exchanged by males and females within the female-defence polygyny of the lizard, Anolis carolinensis . During heterosexual interactions, both sexes performed three kinds of stereotypic headbob displays (A, B, and C) with equal precision. These three display types were essentially identical to A, B, and C display types previously documented for both sexes during consexual contests, and for males when displaying alone (non-directed context). Therefore, there is no courtship-specie c headbob display in A. carolinensis . Although interacting males and females displayed at a similar mean frequency (»20 displays/h), signalling was sexually dimorphic in that: (1) males used predominately C displays (89%), whereas females used predominantly A and B displays (48% and 50%, respectively); (2) males extended their dewlaps with almost every display (98%), whereas females extended their dewlaps with few displays ( <2%); (3) males sequenced 80% of displays in volleys of two or more displays, whereas females performed only 12% of displays in volleys; and (4) males concluded 22% of displays with shudderbobs ( i.e. display modie er composed of shallow, quick, double bobs), whereas females never appended displays with shudderbobs. From e eld and laboratory data on A. carolinensis signal behaviour during other social contexts and the species’ female-defence mating system, we interpret heterosexual signalling from a perspective of intrasexual selection to discuss the: (1) absence

Avoidance learning by the curly-tailed lizard, Leiocephalus schreibersi : implications for anti-predator behavior

Recognition and avoidance of predators is an ecologically relevant task which has been found to have innate components (e.g., Morse, 1970; Curio 1976), especially in the co-evolved relationships where a prey species employs special avoidance behaviors to counter the hunting strategies of a specific predator (e.g., Edmunds, 1974). However, if a species is relatively long-lived and likely to encounter an unpredictable number of life-threatening stimuli, one would expect a selective advantage for individuals which also possess a facility to recognize novel predators through conditioned learning. There are some reliable data on the relative responsiveness of a prey species in learning to recognize a novel predator (e.g., Csanyi, 1985, 1986), but there are no such studies for lizards.

Form emergence and fixation of head bobbing displays in the green anole lizard (Anolis carolinensis): A reptilian model of signal ontogeny.

Signal ontogeny was examined in green anoles (Anolis carolinensis). From 1,246 head bob displays given by 114 juveniles, it was found that juveniles possessed all 3 display types (A, B, and C) described for adults and that C displays were present at hatching, but A and B displays appeared to emerge gradually from a common precursor. Durations of the head bobs and pauses that make up juvenile displays tended to be more variable (i.e., less stereotyped) than those of adult displays. However, within the juvenile class, sex, age (or size), social context, and rearing environment (field or lab) had no effect on display structure or stereotypy. Thus, in contrast to typical signal ontogeny in songbirds and mammals, components of the green anole signal repertoire are expressed from early development. Similar to signal ontogeny in altricial species, maturation is nevertheless important for the complete and stereotyped expression of the adult signal repertoire.

Competitive Interference between the Puerto Rican Lizards, Anolis cooki and A. cristatellus

Anolis cooki and Anolis cristatellus are sympatric lizards engaged in intense interspecific competition. We have identified and analyzed a critical area of competitive interference by measuring various niche dimensions and behavioral interactions under natural conditions. Four study areas of similar habitat composition were established within 5 km of each other: one allopatric for A. cooki, one allopatric for A. cristatellus and two sympatric areas. The variables of cloacal temperatures, perch height, perch diameter and habitat type were compared between lizards in and among the study areas. No significant differences in the variables were found between the sexes of a species or between species on the allopatric areas, nor were there differences between sympatric and allopatric A. cristatellus. Sympatric A. cooki males and females, however, exhibited a significant divergence from their allopatric counterparts by utilizing standing dead vegetation and small bushes rather than larger and more complex microhabitat. This shift was most likely in response to competitive interference from A. cristatellus. Except for sympatric A. cooki, adult males in both the allopatric and sympatric conditions showed a significant and positive correlation between snout-vent lengths and the relative complexity and height of their immediate microhabitat. This suggests that there is intraspecific competition among males, with the larger conspecific males controlling the taller and more complex habitat. Thus when the sympatric male A. cooki occupy small types of microhabitat, they are only likely to encounter the smaller size classes of A. cristatellus males. Intruder-release experiments showed that encounters between male A. cooki and A. cristatellus were very aggressive, similar in intensity to conspecific interactions. Less than one out of two times were resident A. cooki able to evict A.

Male and Female Reproductive Cycles of the Jamaican Lizard, Anolis opalinus

A montane population (elev. 690 m) of the Jamaican lizard, Anolis opalinus, was monitored weekly for 12 months. A greater percentage of reproductive individuals was found year-round than in any previously described anole from a similar latitude and elevation. The high level of annual reproduction occurred in spite of distinct wet-dry periods (171 cm of rain, May-Oct.; and 32 cm of rain, Nov.-April). All males (n = 146) from all months were fully gametogenic. Morphometrics of sexual structures, however, reflected some monthly variance. Mean monthly testis weight showed a 2.2-fold annual range; other measured sex structures fluctuated much less (0.3-0.6-fold). As a group, measured variables reached their maxima during April-July and minima during Oct.-Nov. The testicular cycle was shifted two months in advance of the wet season, with almost no male reproductive structures correlated with the annual cycle of climatic variables. Males showed no tendency to lose weight during their peak reproductive months. Field observations recorded copulations, advertisement displaying, and territorial defense the year-round. For all females (n = 173), the proportion gravid in monthly samples varied from 42% in Dec. to 100% in Aug. Though apparently not initiated by the onset of rain in May, reproductive variables combined to reach their maxima (JuneOct.) during warm wet months. Occurrence of females carrying two oviductal eggs began in April and ceased in Oct.; total oviductal egg volume overlapped the seven months of highest maximum daily temperatures (April-Oct.) and the six months of greatest rainfall (May-Oct.). Large oviductal egg size was associated with large females, but larger females did not appear to produce more eggs than smaller females in either the wet or dry periods. Female reproductive variables reached their greatest levels several months after the male cycle had registered its maxima; no reproductive variables significantly covaried between the sexes.