The endemic insular and peninsular species Chaetodipus spinatus (Mammalia, Heteromyidae) breaks patterns for Baja California

Effects of insularity on genetic diversity within and among natural populations

We conducted a quantitative literature review of genetic diversity (GD) within and among populations in relation to categorical population size and isolation (together referred to as “insularity”). Using populations from within the same studies, we were able to control for between‐study variation in methodology, as well as demographic and life histories of focal species. Contrary to typical expectations, insularity had relatively minor effects on GD within and among populations, which points to the more important role of other factors in shaping evolutionary processes. Such effects of insularity were sometimes seen—particularly in study systems where GD was already high overall. That is, insularity influenced GD in a study system when GD was high even in non‐insular populations of the same study system—suggesting an important role for the “scope” of influences on GD. These conclusions were more robust for within population GD versus among population GD, although several biases might underlie this difference. Overall, our findings indicate that population‐level genetic assumptions need to be tested rather than assumed in nature, particularly for topics underlying current conservation management practices.

A new species and three subspecies of the desert shrew (Notiosorex) from the Baja California peninsula and California

Desert shrews of the genus Notiosorex comprise four species with morphological characteristics that are difficult to distinguish among the species. Indeed, N. cockrumi was described using only genetic markers. Based on molecular divergence documented in N. crawfordi, we hypothesize that a fifth species is present in the Baja California peninsula. Genetic variation at the species level was analyzed using individuals from locations west of the Colorado River in the Baja California peninsula, Mexico, and California, United States. Molecular markers of mitochondrial origin (cytochrome b, 1,140 bp; cytochrome c oxidase subunit I, 542 bp; and cytochrome c oxidase subunit III, 672 bp), as well as the nuclear intron 7 of the beta fibrinogen gene (385 bp) were used to construct a phylogeny for species of the genus Notiosorex. Genetic distances of 12.46–15.58% between west and east of the Colorado River were obtained using p-distance models. Our phylogenetic analyses showed almost identical topologies, placing populations from west of the Colorado River in three monophyletic clades with high bootstrap support values. Results of molecular phylogenetic identity among shrews of the genus Notiosorex support the existence of an undescribed, polytypic species of Notiosorex west of the Colorado River.

Islands in the desert for cavity-nesting bees and wasps: Ecology, patterns of diversity, and conservation at oases of Baja California Peninsula

AIMS

The oases of Baja California Peninsula (BCP) have been proposed as important hotspots of biodiversity that hold an exceptional richness in the middle of desert conditions. We tested the effect of habitat and anthropogenic disturbance on communities of cavity-nesting taxa, with specific emphasis on bees, wasps, and their natural enemies.

METHODS

In oases of BCP and desert neighbor environments, trap-nesting taxa were evaluated in response to factors affecting the nest abundance, richness, and community structure. We used statistical models to find correlates of nest abundance and patterns of diversity, as well as ecological analyses to determine the effect of habitat and human disturbance on species diversity and community structure.

RESULTS

Solar irradiation, distance to a perennial waterbody and relative humidity influenced the presence of nests, number of brood cells, and parasitism. In general, abundance, species richness, and parasitism were higher in oases, especially in those with less human disturbance. Bees did not discriminate between oases and deserts to nest, whereas mud-daubing wasps were more dependent of oases. The degree of anthropogenic disturbance did not affect the occurrence of parasitism, but it had an adverse effect on the parasitism intensity (number of attacked cells). The community structure was more complex and even in oases and low-disturbed sites. The similarity between sites did not exceed 30%, and the proportion of shared species between oases and deserts varied from 2.7% to 26.6%.

MAIN CONCLUSIONS

The oases of Baja California are functioning as mesic islands in the desert, each oasis hosting a unique community of cavity-nesting taxa. About 65% of the nests and 50% of species occurred exclusively in the oasis. Thus, cavity-nesting species that depend on mesic conditions could be threatened if the oases of BCP disappear in the future. Local conditions in the oases and deserts of the BCP are shaping the community structure. However, large-scale factors such as climate can influence the seasonality and occurrence of species within the community of cavity-nesting dwellers. Since habitat loss and fragmentation can degrade the oases' functionality, strategies to maintain the ecosystem services of pollination and biological control should be included in the conservation programs of these fragile habitats.

Do island populations differ in size and shape compared to mainland counterparts?

Adaptation and evolution of terrestrial vertebrates inhabiting islands have been the topic of many studies, particularly those seeking to identify trends or patterns in body size in mammals, albeit not necessarily in shape, in relation to mainland populations. The spiny pocket mouse, Chaetodipus spinatus, is distributed in the Baja California peninsula and its surrounding islands. Insular populations became isolated ~12,000 due to changes in sea level; these populations’ matrilinear (mitochondrial) DNA shows minor interpopulation variation. We tested the hypothesis that adaptation and evolution in these island populations involve variation in both skull size and skull shape (using geometric morphometrics) relative to mainland populations, rather than only in size as previously assumed. A total of 363 specimens from 15 insular and peninsular populations were used in analysis of the skull length and geometric morphometric analyses. Our findings revealed significant differences related to skull size among population. The skull shape analyses showed two significantly different morphotypes: one for all island specimens and one for all mainland samples. Our analyses support the hypothesis that insular populations may not only vary in size relative to mainland populations, but may also show variations in shape, regardless of differing conditions across islands.

Rediscovery of the extinct Tule shrew (Sorex ornatus juncencis) in the San Quintin plains: a taxonomic reevaluation after 90 years without new records

In this study, we investigate the geographic distribution of the Tule shrew (Sorex ornatus juncensis), an endemic subspecies of the San Quintin plains associated with coastal vegetation. Records on this shrew are scarce; herein, we provide knowledge about its current conservation status and report the presence of one Tule shrew specimen, something that has not happened since 1926. The distribution of the Tule shrew is associated with coastal vegetation, limited to the San Quintin plains, with scarce records. Field trips were conducted during 2013–2015 in the San Quintin plains and San Pedro Martir range of the Baja California Peninsula. The sampling effort was 3250 trap nights. One specimen of S. o. juncensis was recorded in association with coastal sage-scrub vegetation and identified following the original description, based on its narrower skull relative to Sorex ornatus ornatus. We used a mitochondrial cytochrome b gene sequence (384 bp) to confirm this identification and compare genetic distances using the Kimura’s two-parameter nucleotide substitution model vs. other populations of the ornatus group. We found a genetic divergence of less than 1.0% based on sequences from specimens collected from Sierra San Pedro Martir, El Rosario and Sierra La Laguna. In the locality of the S. o. juncensis specimen collected, the original vegetation consists of patches of coastal scrubs, which cover an area of less than 1 km2, affected by agriculture and habitat fragmentation. We reallocated the taxonomic level of the Tule shrew inhabiting the plains of San Quintin in the Baja California Peninsula to subspecies as S. o. juncensis based on geographic isolation, morphometric characteristics and coloration differences vs. S. o. ornatus. The population inhabiting San Quintin plains is subjected to strong pressure due to habitat loss.