The efects of global warming on populations of the species complex Tropidurus torquatus (Squamata:Tropiduridae) in Brazil

Author(s)

Carla Piantoni

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2015-11-27

Examining board members

Carlos Arturo Navas Iannini; Fernando Ribeiro Gomes; Renata Brandt Nunes; Marco Aurélio de Sena

• Advisor: Carlos Arturo Navas Iannini; Nora Ruth Ibargüengoytía

Abstract

In Brazil, an increase in the mean air temperature (Ta) of up to 6°C and a trend of decreasing rainfall by 5−20% are expected within 85 years. Climate warming is expected to overrun local adaptation and survival will depend on the plasticity and dispersal options and abilities. Predicting how organisms will respond these changes is one of the most critical challenges for contemporary ecophysiologists. Lizards are particularly sensitive to global warming, as temperature changes could shift overall performance to suboptimal levels, restricting time for activity. The low resilience to environmental changes of lineages from regions of low climatic variability (close to the Equator) combined with low dispersal options and current habitats’ Ta that exceeds their thermal optima, among other factors, make these populations the most vulnerable to warming. We conducted spatial and temporal analyses to assess the vulnerability of populations of the Tropidurus torquatus species complex in the Brazilian Cerrado and whether resilience is influenced by the magnitude of flexibility in thermal physiology and performance that exists within populations using three different approaches: (1) we compare data on body (Tb) and operative temperatures (Te, “null temperatures” for nonregulating animals), preferred body temperatures (mean T/p and Tset Tet range), and quantitative indices of temperature regulation and quality of the thermal environment (b, d e and E) for Tropidurus with data from the literature for Anolis, Liolaemus, and Sceloporus, and for 60 populations of 21 species of tropidurids from the Caatingas, Amazonia, Cerrado, Chaco, and other regions as the coast of Peru and Galapagos Islands; (2) We analyze patterns of variability in the performance capacities for velocity and endurance within and among populations of T. torquatus, T. oreadicus, T. etheridgei and T. catalanenis, and estimate the impact of a Ta increase by 3°C on performance and activity of these lizards in a warming scenario; and (3) we examine the geographic and temporal variation of individual age, growth rates, age at sexual maturity and longevity in specimens of T. torquatus at two sites at different latitudes; temporal variation was estimated studying subsamples at each site collected in 1960s and 2012, whereas the geographical comparisons were performed between the two subsamples collected in 2012 both at the two sites. Our results confirm the hypotheses by suggesting that thermoregulatory behavior increases with latitude and altitude and that tropical and lowland lizards behave as thermoconformers. We estimate that tropical populations with poor or no thermoregulatory behavior that inhabit stressful environments (open and low elevation sites) are the most vulnerable to rising temperatures. In contrast, Patagonia steppe and mountains as well as other montane environments represent future thermal refuges for lizards that would eventually be forced to retreat to these environments. Within tropidurids, a general pattern suggests that the thermoregulatory behavior decreases towards the Equator, particularly due to environmental constrains and probably to the low environmental variation. In most lineages, similar and higher Tb and Tp with respect to Ta point to a plesiomorphic condition, probably related to earlier forested environments. Constraint or no thermoregulation combined with the large proportions of Tb and Te above the thermal optima augment the risk of overheating and preclude time of activity particularly in the central and northernmost regions of the Cerrado. Based on the thermal performance curves, thermal breadths (B80’s) and safety margins increased with the thermal variation and decreased with the variation of annual precipitation. The results on the temporal variation and between sites differences on the growth patterns suggest that warming positively affect growth in T. torquatus. The increase of Ta of the last decades accelerated growth rates, anticipated sexual maturity and shortened the life−span at both sites. Although short-term effects of an increasing Ta’s may seem beneficial with respect to growth and reproduction, we predict an overall decay in the fitness response in all populations in the long term. Due to the large proportions of T e ’s currently exceeding the upper limit of the B 80 and thermal preferenda of T. torquatus and T. etheridgei at the Central site and the limited dispersal capacity and low variability on the thermal biology of T. torquatus in the warm gallery forest, the northernmost and Central populations are expected to experience the highest impact. (AU)