Sergio Ticul Álvarez-Castañeda

Current status of rodents on islands in the Gulf of California

On islands in the Gulf of California, many species and subspecies of rodents are relict species, restricted to the islands, and now considered extinct or verging on extinction. From 1991 to 1999, each island was surveyed and an average of 15 work-nights were spent on each island, for a total of 15,000 trap-nights. A Fourier series was used to estimate population density. Five native taxa are now considered extinct (Chaetodipus baileyi fornicatus, Peromyscus guardia mejiae, P. g. harbinsoni, P. pembertoni, and Neotoma bunkeri). Two species are at risk of extinction (Dipodomys insularis and Neotoma albigula varia). The most probable cause for extinction is the introduction of nonnative species, specifically cats. We believe that the most vulnerable rodent populations of the islands in the Gulf of California to non-native species are Neotoma lepida latirostra on Danzante island and Neotoma lepida abbreviata on San Francisco island, both in the state of Baja California Sur.

Geographic genetic architecture of pocket gopher (Thomomys bottae) populations in Baja California, Mexico.

Phylogenetic analyses of complete mitochondrial cytochrome b sequences support the monophyly of pocket gopher (Thomomys bottae) populations from the 1000 km length of the Baja California peninsula of Mexico, relative to other geographical segments of the species range in western North America. The Baja California peninsula is an area that encompasses considerable ecomorphological and infraspecific diversity within this pocket gopher species. However, detailed population analyses encompassing 35 localities distributed over the southern half of the peninsula reveal only trivial phylogeographical structure. Rather, most of the 72 unique 500‐base pair haplotypes examined from 142 individuals is restricted to single populations, although a few haplotypes are shared broadly across geography. Individual populations are typically comprised of haplotype sets from different branches in a network of relationships. Analysis of molecular variance (amova) indicates that approximately half of the total pool of variation is contained among individuals within local populations, and that only about 25% can be explained by the regional subdivisions of current subspecies distributions or physiographic realms. A hypothesized historical vicariant event that has been causally linked to the phylogeographical structure of other, codistributed species has had little influence on these pocket gopher populations, explaining only 13% of the total variation. The temporal depth, estimated by coalescence parameters, of the haplotype lineage in Baja California is relatively recent, approximately 300 000 generations; both the mismatch distribution of pairwise comparisons and a significantly positive exponential growth estimate support a recent history of expanding populations; but current, or recent past, migration estimates have remained small, are largely unidirectional from north to south, and weak isolation by distance is present. All data suggest that pocket gophers have relatively recently invaded the southern half of peninsular Baja California, with the genetic signature of expansion still evident but with sufficient time having lapsed to result in a weak isolation by distance pattern. The geographical assemblage of sampled populations thus appears as a meta‐population, with limited gene flow contrasting with random haplotype loss due to drift in small, localized populations.

EVOLUTIONARY RELATIONSHIPS OF WHITE-FOOTED MICE (PEROMYSCUS ) ON ISLANDS IN THE SEA OF CORTEZ, MEXICO

Abstract Sixteen populations of Peromyscus on islands in the Sea of Cortéz (= Gulf of California), Mexico, were compared with 9 mainland species of Peromyscus based on sequence data for a 699-base-pair fragment of the mitochondrial DNA (mtDNA) COIII gene. An unrooted neighbor-joining tree based on corrected pairwise estimates of sequence divergence among variable mtDNA haplotypes indicated a recent (late Pleistocene) origin from a source on the adjacent mainland for 10 island forms representing P. boylii, P. crinitus, P. eremicus, P. eva, P. fraterculus, and P. maniculatus. Five other populations did not seem to be derived from species currently on the nearest mainland, suggesting overwater dispersal or distributional changes on the mainland after drowning of land-bridge connections. One population, possibly of more ancient origin, on Isla Cerralvo near the Baja California peninsula, probably originated via trans-Gulf rafting from the Sonoran mainland. Based on these results, 4 insular species (P. stephani, P. interparietalis, P. caniceps, and P. dickeyi) should be considered subspecies of P. boylii, P. eremicus, P. fraterculus, and P. merriami, respectively. The emergent view of evolutionary relationships within the subgenus Haplomylomys in the region reflects pre-Pleistocene phylogeographic events on the mainland surrounding the Gulf and a more recent origin of island populations.

Phylogenetic structure of the Thomomys bottae–umbrinus complex in North America

The phylogeography of the Thomomys bottae-umbrinus complex in the United States and Mexico was assessed with sequences of the mitochondrial cytochrome b gene. These sequences were obtained from 225 individuals representing 108 locations over the range, including 56 sequences from GenBank. 110 (500bp) sequences were used for Bayesian inference and neighbor-joining analyses, and 34 (1140bp) specimens from the main clades obtained from the Bayesian inference were used in maximum-parsimony and maximum-likelihood analyses. The different analyses indicate significant variation within the species complex that averages 13% among major groups of genetic differences among Thomomys bottae-umbrinus. The overall pattern of geographic variation is not concordant with the current taxonomy. To the contrary, eight monophyletic groups are supported by all analyses and can be considered phylogenetic species. Overall divergence among these groups appears influenced by historical biogeographic events active during the Pliocene and Pleistocene.

STATUS OF DIPODOMYS INSULARIS, AN ENDEMIC SPECIES OF SAN JOSÉ ISLAND, GULF OF CALIFORNIA, MEXICO

Abstract The islands of the Gulf of California are considered protected natural areas by the Mexican government. However, mammals in these islands face major threats and possible extinction because of the introduction of exotic species. Dipodomys insularis is endemic to San José Island, and has been declared a critically endangered species by the World Conservation Union. Surveys undertaken since 1989 had been unsuccessful in documenting the presence of this species, leading to the conclusion that extinction may have occurred because of the presence of feral cats on the island. After 15 years of unsuccessful surveys, we rediscovered D. insularis in 2005. Kangaroo rats were captured at 5 locations on the island within a total area of less than 30 km2. Fecal analyses showed that D. insularis is not a usual prey item of feral cats. A discriminant function analysis allocated 99.29% of the heteromyid upper incisors recovered from scats to Chaetodipus spinatus (P > 0.97), whereas only 2 incisors (0.71%) were allocated to D. insularis. The actual extent of damage to the native biota caused by the introduction of cats remains unknown.

Systematics of the antelope ground squirrel (Ammospermophilus) from islands adjacent to the baja California Peninsula

Abstract I assessed the systematics of Ammospermophilus leucurus from the islands of Espíritu Santo and San Marcos adjacent to the Baja California peninsula, using sequences of the mitochondrial cytochrome-b (Cytb) gene and morphological analyses from the island and the peninsular samples. For the molecular analysis, the Cytb gene (500 base pairs) was sequenced from individuals from 34 different localities. Maximum-parsimony, maximum-likelihood, and neighbor-joining analyses indicated a phylogenetic break in the central part of the Baja California peninsula. Samples from the islands of Espíritu Santo and San Marcos were grouped with the southern clade with an average of 1.2 substitutions that separated adjacent haplotypes in a network. Two haplotypes occurred on San Marcos Island; one was unique and the other also was present in peninsular samples. The only haplotype found on Espíritu Santo Island also occurred on the peninsula. Both univariate and multivariate morphometric analyses and the pattern of presence–absence of the 3rd upper premolar distinguished samples from Espíritu Santo and the Cape region of the peninsula but not between San Marcos Island and Francisco de la Sierra on the peninsula. Thus, the San Marcos Island ground squirrel could not be distinguished from those of the peninsula and should be recognized as the same subspecies that occupies the adjacent peninsular areas (A. leucurus extimus). In addition, neither molecular nor morphological data supported the recognition of A. insularis (from Espíritu Santo Island) as a distinct species from peninsular samples of A. leucurus, although this taxon showed morphological differentiation in dental characters that still support its recognition as a valid subspecies (A. leucurus insularis).

Revision of the Dipodomys Merriami Complex in the Baja California Peninsula, Mexico

Abstract The kangaroo rat Dipodomys merriami occurs widely over the Baja California peninsula, inhabiting all the arid and sandy lowlands. Its range encompasses diverse climatic, edaphic, and vegetation zones, including 2 islands. The 11 taxa recognized in the merriami complex in this region almost 50 years ago remain valid to the present. The 2 island forms originally were described as different species, and have been treated in different ways by subsequent authors. In this investigation we used a genetic analysis of 2 mitochondrial genes, cytochrome b (Cytb) and cytochrome c oxidase subunit III (COIII), to study patterns of genetic structuring in this species throughout the peninsula. We supplemented existing morphometric and pelage color data with new data, and integrated these data sets into a phylogenetic analysis. Finally, we explored how our results compared with the existing taxonomic arrangement of species and subspecies. Our phylogenetic analyses of molecular data used the concatenation of 1,140 base pairs (bp) of the Cytb gene and 690 bp of the COIII gene; cladograms were generated using maximum-parsimony, maximum-likelihood, and Bayesian inference procedures. A hierarchy of nested clades was produced, the highest level of which revealed 2 reciprocally monophyletic clades separated by 20 mutational steps. There is a Southern Clade extending north to the Vizcaíno Desert in the west and San José Island in the east, and a Northern Clade that includes all the populations farther to the north. At a shallower level, the Southern Clade contains 4 subclades, including the populations of San José and Margarita islands, whereas the Northern Clade is composed of 3 subclades. Adding the morphometric and pelage coloration data sets to the analyses resulted in support for the 11 previously recognized taxa arranged in a single species, Dipodomys merriami, but with improved understanding of how the subspecies relate to each other. As is increasingly appreciated, our investigation supports a comprehensive approach involving multiple data sets that are sensitive to a wide temporal range of evolutionary history for phylogenetic reconstruction.

TAXONOMIC REVISION OF THOMOMYS BOTTAE IN THE BAJA CALIFORNIA SUR LOWLANDS

Abstract The populations of Thomomys bottae in the southern part of the Baja California peninsula have been assigned to several subspecies, mainly because they are isolated and show some morphological differences. In order to assess the status of T. bottae in Baja California, we conducted a survey in all the possible habitats in lowlands of the southern part of the peninsula by collecting specimens and obtaining tissues for genetic analyses. From the 6 subspecies of T. bottae present in Baja California Sur, 560 specimens were collected from 42 localities. A continuous geographical distribution among all the previously described isolate subspecies was confirmed and analysis of variance, analysis of molecular variance, and phylogentic analyses do not show morphologic or genetic differences among groups of the subspecies T. b. anitae, T. b. imitabilis, T. b. incomptus, T. b. litoris, and T. b. magdalenae from the lowlands south of the Vizcaino Desert. Thus, we conclude that these are junior synonyms of T. b. anitae. T. bottae russeolus in the Vizcaino Desert is sufficiently morphologically, morphometrically, and genetically different to be considered as a distinct subspecies.

New perspectives on trophic guilds of arthropodivorous bats in North and Central America

Trophic guilds are useful concepts for advancing our knowledge of trophic structure of communities, dynamics of species interactions, redundancy in ecosystem services, resilience to disturbances, response to climate change, conservation strategies, etc. For insectivorous bats, current literature suggests 8 trophic-related guilds. These include 3 guilds based on the openness of foraging areas, 3 based on the style of feeding, and 2 recently proposed subguilds among gleaners. Some gleaners are “passive,” using densely cluttered vegetation in which echolocation is ineffective, and others are “actively” gleaning, using echolocation to procure prey. None of these guilds is based on the actual diets of bats. We analyzed 33 reports of diet composition representing 51 species of arthropod-feeding bats inhabiting North and Central America. We wanted to determine if the classical guild structure was concordant with the actual diets of bats and to compare guild structure in the Nearctic with that in the Neotropics. Discriminant function and principle component analyses generated 5 groups of genera based on the proportion of various arthropod taxa (mainly orders) in their diets. These groups were very different from classical guilds and showed almost no overlap among bat genera between the 2 continental regions. A similar analysis based on prey flying ability and hardness of their exoskeletons suggested 4 guilds that were more consistent with classical guild concepts, had higher rates of unambiguous guild assignment, and also showed major continental differences. Our results suggest a new arrangement of 4 guilds for arthropod-feeding bats in North and Central America that are based primarily on 2 features of their prey. New molecular techniques should allow us to build on this arrangement by significantly improving the taxonomic level of prey identification.

Conservation status of the threatened, insular San Jose brush rabbit ( Sylvilagus mansuetus )

ABSTRACT. The conservation status and distribution of the insular endemic San Jose brush rabbit (Sylvilagus mansuetus), as well as threats to its population viability, were determined through surveys undertaken since 1995 on San José Island in the Gulf of California, Mexico. Sylvilagus mansuetus is restricted to a specific desert habitat found in the southwestern coastal plains of the island. Vegetation in this habitat is composed primarily of 7 plant species. The extent of rabbit occurrence is only 20 km2, and the population density estimate in the most optimal habitat is 25–35 individuals · km-2. To our knowledge, the San Jose brush rabbit possesses the smallest distribution among all lagomorph species. Sylvilagus mansuetus is threatened by a population of feral cats and by human activities, including illegal hunting, development of a tourist area, and a salt mine. Human activities, even over a short time frame, could severely impact this restricted area and endanger the survival of this species. Recommended management includes removing cats and conducting additional research on the rabbits life history and ecology.