Carlos García-Robledo

DNA barcodes for ecology, evolution, and conservation.

The use of DNA barcodes, which are short gene sequences taken from a standardized portion of the genome and used to identify species, is entering a new phase of application as more and more investigations employ these genetic markers to address questions relating to the ecology and evolution of natural systems. The suite of DNA barcode markers now applied to specific taxonomic groups of organisms are proving invaluable for understanding species boundaries, community ecology, functional trait evolution, trophic interactions, and the conservation of biodiversity. The application of next-generation sequencing (NGS) technology will greatly expand the versatility of DNA barcodes across the Tree of Life, habitats, and geographies as new methodologies are explored and developed.

Tropical Plant–Herbivore Networks: Reconstructing Species Interactions Using DNA Barcodes

Plants and their associated insect herbivores, represent more than 50% of all known species on earth. The first step in understanding the mechanisms generating and maintaining this important component of biodiversity is to identify plant-herbivore associations. In this study we determined insect-host plant associations for an entire guild of insect herbivores using plant DNA extracted from insect gut contents. Over two years, in a tropical rain forest in Costa Rica (La Selva Biological Station), we recorded the full diet breadth of rolled-leaf beetles, a group of herbivores that feed on plants in the order Zingiberales. Field observations were used to determine the accuracy of diet identifications using a three-locus DNA barcode (rbcL, trnH-psbA and ITS2). Using extraction techniques for ancient DNA, we obtained high-quality sequences for two of these loci from gut contents (rbcL and ITS2). Sequences were then compared to a comprehensive DNA barcode library of the Zingiberales. The rbcL locus identified host plants to family (success/sequence = 58.8%) and genus (success/sequence = 47%). For all Zingiberales except Heliconiaceae, ITS2 successfully identified host plants to genus (success/sequence = 67.1%) and species (success/sequence = 61.6%). Kindt’s sampling estimates suggest that by collecting ca. four individuals representing each plant-herbivore interaction, 99% of all host associations included in this study can be identified to genus. For plants that amplified ITS2, 99% of the hosts can be identified to species after collecting at least four individuals representing each interaction. Our study demonstrates that host plant identifications at the species-level using DNA barcodes are feasible, cost-effective, and reliable, and that reconstructing plant-herbivore networks with these methods will become the standard for a detailed understanding of these interactions.

Limited tolerance by insects to high temperatures across tropical elevational gradients and the implications of global warming for extinction

Significance Tolerance to high temperatures will determine the survival of animal species under projected global warming. Surprisingly little research has been conducted to elucidate how this trait changes in organisms living at different elevations of similar latitudes, especially in the tropics. DNA barcodes demonstrate that insect species previously thought to have broad elevational distributions and phenotypically plastic thermal tolerances actually comprise cryptic species complexes. These cryptic species occupy discrete elevational ranges, and their thermal tolerances seem to be locally adapted to temperatures in their life zones. The combination of high species endemism and local adaptation to temperature regimes may increase the extinction risk of high-elevation insects in a warming world. The critical thermal maximum (CTmax), the temperature at which motor control is lost in animals, has the potential to determine if species will tolerate global warming. For insects, tolerance to high temperatures decreases with latitude, suggesting that similar patterns may exist along elevational gradients as well. This study explored how CTmax varies among species and populations of a group of diverse tropical insect herbivores, the rolled-leaf beetles, across both broad and narrow elevational gradients. Data from 6,948 field observations and 8,700 museum specimens were used to map the elevational distributions of rolled-leaf beetles on two mountains in Costa Rica. CTmax was determined for 1,252 individual beetles representing all populations across the gradients. Initial morphological identifications suggested a total of 26 species with populations at different elevations displaying contrasting upper thermal limits. However, compared with morphological identifications, DNA barcodes (cytochrome oxidase I) revealed significant cryptic species diversity. DNA barcodes identified 42 species and haplotypes across 11 species complexes. These 42 species displayed much narrower elevational distributions and values of CTmax than the 26 morphologically defined species. In general, species found at middle elevations and on mountaintops are less tolerant to high temperatures than species restricted to lowland habitats. Species with broad elevational distributions display high CTmax throughout their ranges. We found no significant phylogenetic signal in CTmax, geography, or elevational range. The narrow variance in CTmax values for most rolled-leaf beetles, especially high-elevation species, suggests that the risk of extinction of insects may be substantial under some projected rates of global warming.

The genus Cephaloleia Chevrolat, 1836 (Coleoptera, Chrysomelidae, Cassidinae)

Abstract The species of the Neotropical genus Cephaloleia Chevrolat, 1836 are revised. We present a key to the known larvae of Cephaloleia (8 species), a key to the 95 species known to occur in Mexico, Central America and the West Indies, and a key to the 138 species known to occur in South America. All identification keys were translated to Spanish. Descriptions for the 214 known species of Cephaloleia as well as illustrations for 212 species are presented. The following species are removed from Cephaloleia: C. bipartita Pic, 1926c is transferred to Hybosispa Weise, 1910; C. minasensis Pic, 1931 and C. viridis Pic, 1931 are transferred to Stenispa Baly, 1858. The following species are described as new: C. abdita sp. n. from Brazil; C. amba sp. n. from Colombia, Ecuador, and Peru; C. angustacollis sp. n. from Ecuador; C. brevis sp. n. from French Guiana; C. calathae sp. n. from Costa Rica; C. chica sp. n. from Peru; C. conforma sp. n. from Costa Rica; C. crenulata sp. n. from Ecuador; C. gemma sp. n. from Bolivia and Brazil; C. horvitzae sp. n. from French Guiana; C. interrupta sp. n. from Costa Rica; C. kressi sp. n. from Costa Rica; C. lenticula sp. n. from Ecuador, French Guiana, Peru, and Suriname; C. nana sp. n. from Ecuador; C. ochra sp. n. from Ecuador; C. stainesi sp. n. from Costa Rica; and C. susanae sp. n. from Brazil and Ecuador. Cephaloleia simoni Pic, 1934 is treated as Incertae sedis. The larvae of C. erichsonii Baly, 1858 and C. puncticollis Baly, 1885 are described and illustrated.

Lower thermal tolerance in nocturnal than in diurnal ants: a challenge for nocturnal ectotherms facing global warming

1. The thermal adaptation hypothesis proposes that because thermoregulation involves a high metabolic cost, thermal limits of organisms must be locally adapted to temperatures experienced in their environments. There is evidence that tolerance to high temperatures decreases in insects inhabiting colder habitats and microclimates. However, it is not clear if thermal limits of ectotherms with contrasting temporal regimes, such as diurnal and nocturnal insects, are also adapted to temperatures associated with their circadian activities.

Experimental assemblage of novel plant-herbivore interactions: ecological host shifts after 40 million years of isolation

Geographic isolation is the first step in insect herbivore diet specialization. Such specialization is postulated to increase insect fitness, but may simultaneously reduce insect ability to colonize novel hosts. During the Paleocene-Eocene, plants from the order Zingiberales became isolated either in the Paleotropics or in the Neotropics. During the Cretaceous, rolled-leaf beetles diversified in the Neotropics concurrently with Neotropical Zingiberales. Using a community of Costa Rican rolled-leaf beetles and their Zingiberales host plants as study system, we explored if previous geographic isolation precludes insects to expand their diets to exotic hosts. We recorded interactions between rolled-leaf beetles and native Zingiberales by combining DNA barcodes and field records for 7450 beetles feeding on 3202 host plants. To determine phylogenetic patterns of diet expansions, we set 20 field plots including five exotic Zingiberales, recording beetles feeding on these exotic hosts. In the laboratory, using both native and exotic host plants, we reared a subset of insect species that had expanded their diets to the exotic plants. The original plant-herbivore community comprised 24 beetle species feeding on 35 native hosts, representing 103 plant-herbivore interactions. After exotic host plant introduction, 20% of the beetle species expanded their diets to exotic Zingiberales. Insects only established on exotic hosts that belong to the same plant family as their native hosts. Laboratory experiments show that beetles are able to complete development on these novel hosts. In conclusion, rolled-leaf beetles are pre-adapted to expand their diets to novel host plants even after millions of years of geographic isolation.

Low quality diet and challenging temperatures affect vital rates, but not thermal tolerance in a tropical insect expanding its diet to an exotic plant

Determining responses of organisms to changing temperatures is a research priority, as global warming threatens populations and ecosystems worldwide. Upper thermal limits are frequently measured as the critical thermal maximum (CTmax), a quick bioassay where organisms are exposed to increasing temperatures until individuals are not able to perform basic motor activities such as walking or flying. A more informative approach to understand organism responses to global warming is to evaluate how vital rates, such as growth or survival, change with temperatures. The main objectives of this study are: (1) to determine if factors affecting insect vital rates such as diet quality, developmental temperatures or acclimation also affect CTmax and (2) to determine if vital rates of different life stages (i.e., insect larvae or adults) display different responses to temperature changes. If different life stages have particular thermal requirements, this may indicate different susceptibility to global warming. This study focuses on Cephaloleia belti (Coleoptera: Chrysomelidae), a tropical insect currently expanding its diet to an exotic host plant. We determined how high and low-quality diets (i.e., native vs novel host), as well as exposure temperatures affect CTmax of adult beetles. We also estimated larval and adult survival when feeding on high and low quality host plants, when exposed to temperatures typical of the elevational distribution of this species, or when exposed to projected temperatures in 100 years. We did not detect an effect of diet quality or acclimation on CTmax. However, larvae and adults had different thermal requirements. CTmax is not affected by previous diet or acclimation as an adult. We propose that to understand processes involved in the adaptation and persistence of ectotherm populations in a warming world, studies must explore responses beyond CTmax, and focus on the response of vital rates to changing temperatures.

First Record of the Genus Chelobasis Gray, 1832 (Coleoptera: Chrysomelidae: Cassidinae) in Mexico (North America)

The Neotropical genus Chelobasis Gray, 1832 (Coleoptera: Chrysomelidae: Cassidinae) includes four known species: Chelobasis aemula (Waterhouse) from Ecuador; Ch. bicolor Gray from Bolivia to Nicaragua; Ch. laevicollis (Waterhouse) from Colombia; and Ch. perplexa (Baly) from Ecuador to Costa Rica. Chelobasis beetles are also known as the “rolled-leaf ” beetles because their larvae and adults feed on the scroll formed by the young leaves of their host plants (Strong and Wang 1977) in the genus Heliconia L. (Heliconiaceae) (GarcíaRobledo et al. 2010). The known northern limit of Chelobasis is Guatemala, where a single individual of Ch. perplexa was collected at the Municipality of Chimaltenango, 14°39′ N, 90°49′ W, ca. 1,800 m elevation (Staines 2009). Here we report the presence of the genus Chelobasis in the Sierra de Los Tuxtlas, Mexico. During June 2014, we surveyed 50 individuals of Heliconia uxpanapensis C. Gut. Báez, an understory herb common in the forest and trail sides of Los Tuxtlas Biological Station, a tropical rainforest