No abstract

During the mating season, male tarantulas abandon their burrows and actively search for widely distributed females, which remain fossorial. As a result, males are exposed to larger fluctuations in environmental conditions without the protection of a permanent retreat. Body temperatures (Tb) of active male tarantulas (Aphonopelma anax) encountered fortuitously in the field ranged from 24.7 to 35.1°C and preferred Tb's measured in a laboratory thermal gradient ranged from 22.1 to 31.3°C. The thermal options available to males at random points in their environment varied substantially throughout the day but temperatures typically exceeded 40°C. In comparison, temperatures within burrows remained below 40°C. Indices calculated from these temperature data suggested that males thermoregulated effectively during the day, while environmental temperatures were within their preferred Tb range at night and so active regulation of Tb was unnecessary. In addition, I determined the exact times that males ceased locomotory activity in the morning (retreat) and when they started activity in the evening (emergence). Data from 23 radio-tagged males indicated that they retreated into temporary burrows between 06:47 and 10:53 CST. Activity commenced again between 16:36 and 20:53 CST as temperatures approached their preferred or selected Tb range.

No abstract

Despite their general notoriety and popularity as pets, little is known of the behavioural ecology of ‘tarantulas’ or theraphosid spiders. We studied a theraphosid of the Arizona deserts, Aphonopelma sp., to determine behavioural events crucial to successful courtship and mating. Males search for spatially scattered females and, at short range, may detect females by substrate‐borne cues. When two males are present with a single female, no direct competition such as aggression is observed. Both males may mate with a single female in rapid succession, with no evidence of post‐copulatory mate guarding. Despite the potential for sexual cannibalism, courtship and mating behaviour patterns exhibit few aggressive elements and males nearly always survive sexual encounters with females. The mating system of this Aphonopelma species may best be described as a type of scramble‐competition polygyny, in which the ability of males to locate receptive females is an important determinant of mating success in males. Multiple mating by females renders predictions concerning fertilization success uncertain, due to the possibility of sperm competition and ‘cryptic’ female mate choice.

Tarantulas exhibit sexual dimorphism in their resting metabolic rate (RMR). The significantly higher RMRs observed in sexually mature males may be an adaptive strategy to support their higher energetic demands when searching for females. In this study, we investigated how intrasexual differences in male RMR may affect their locomotory activity and behavior during the mating season. Over a 2-year period, we radio-tagged male Texas tan tarantulas ( Aphonopelma anax (Chamberlin, 1940)), measured their movements, and periodically recorded their metabolic rates in an open-flow respirometery system over the course of the breeding season. Differences found in search speed, search-area size, and movement patterns were not sufficiently explained by the small amount of intrasexual variation exhibited in RMR. Individuals were capable of searching areas up to 29 ha and moved up to 365 m/day. In addition, metabolic rate measured over a 24 h period showed no circadian periodicity and remained constant over the season. Lastly, the body condition of new captures stayed constant throughout the season, corroborating observations of males feeding and drinking.