Thermal ecology of male tarantulas (Aphonopelma anax) during the mating season

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.

Effect of temperature on leg kinematics in sprinting tarantulas (Aphonopelma hentzi): high speed may limit hydraulic joint actuation

“…These temperatures included the maximum range at which the tarantulas moved in preliminary trials and also encompassed the range of body temperatures recorded in the congener Aphonopelma anax (Shillington, 2002).…”

“…In the current study, we examined the locomotion of tarantulas in the laboratory across their ecologically relevant temperature range (15-40°C; Shillington, 2002). Tarantulas are large-bodied spiders (family Theraphosidae) that locomote readily in captivity (Shillington and Peterson, 2002).…”

“…Their large size facilitates video recording and analysis of their joint kinematics during running (Figs 1, 2). In addition, tarantulas in the wild can experience wide variation in environmental temperatures (Shillington, 2002), so the thermal sensitivity of locomotion is directly relevant to their field ecology. During sprinting in a tarantula, joints extended by hemolymph pressure are characterized by internal volume change during movement (Blickhan and Barth, 1985).…”

“…These two hypotheses are not mutually exclusive, but rather address the possible constraints of using hydraulics for joint extension. To test our hypotheses, we quantified the joint kinematics of tarantulas sprinting, a maximal behavior (Prestwich, 1988), over the entire range of their ecologically active temperatures (Shillington, 2002).…”

An automated temperature-based option for estimating surface activity and refuge use patterns in free-ranging animals

“…Moreover, the small size of the temperature logger (3 g) and quadrupled memory capacity (Thermochron iButton model DS1922L offers 8kB of memory) increase the versatility of TBAE for use in a variety of active foraging species that rely on thermally insulated refugia-like red foxes (Vulpes vulpes), badgers (Meles meles), and cactus wrens (Campylorhynchus brunneicapillus) (Fenn and MacDonald, 1995;Moore and Roper, 2003;Ricklefs and Hainsworth, 1968). Arid environments offer ideal conditions in which to use TBAE since (1) the refugia of resident animals as diverse as arachnids (Polis, 1980;Shillington, 2002), birds (Ricklefs and Hainsworth, 1968), mammals (Jackson et al, 2002;Moore and Roper, 2003;Randall, 1993;Rezende et al, 2003), and reptiles; (Beck and Jennings, 2003;Bradshaw, 1997;Bulova, 2002;Grant and Dunham, 1988) are notably buffered from extreme fluctuations in T air , and thus present the thermal dichotomy required for TBAE and (2) many animals use water-conserving behaviors, including extended inactivity periods and temporally constrained activity (i.e., nocturnality), which improve the accuracy of TBAE (this study). TBAE can also identify the date and time of key annual events such as initiation and cessation of seasonal dormancy (J.…”