Baja California Populations Research Articles

Liver Protein Comparisons of Warm‐adapted Versus Cold‐adapted Populations of Threespine Sticklebacks (Gasterosteus aculeatus)

This study investigated the molecular phenotypes of a warm‐adapted population of threespine sticklebacks (Gasterosteus aculeatus). We created a liver protein assay consisting of 1,016 proteins with Skyline (MacCoss Lab) from four populations (N=24) using data dependent acquisition (DDA) shotgun proteomics. This assay will be used to perform targeted proteomics on future comparisons, which will allow for more precise identification and quantification of the targeted proteins. A population of sticklebacks from Baja California, Mexico is surviving and breeding at temperatures near 30 degrees Celsius, which is close to the upper thermal limit for this species. Understanding what this population is doing at the molecular level to function at these high temperatures may give insight into mechanisms that have allowed for their survival, as well as the potential for other populations to adapt to higher temperatures. Livers from sticklebacks of the Baja California population were then compared to three cold‐adapted populations using gel‐free quantitative proteomics by liquid chromatography‐mass spectrometry (LC‐MS/MS). A resident marine population (Bodega Harbor, CA), a freshwater population (Lake Solano, CA), and an anadromous population (Anchorage, Alaska) were used in these comparisons. Six Baja California threespine sticklebacks and six fish from each of the other three groups were compared in four separate sets (N=96). Approximately 20 proteins were significantly more abundant in the Baja California population than the other three populations across all four sets. Our results suggest that certain molecular chaperones and redox/antioxidant proteins may contribute to the survival of the Baja California population. Our study lays the foundation for highly accurate quantification of protein differences in future comparisons using targeted proteomics. This study also highlights proteins that are consistently found at higher abundance in the warm‐adapted population and thus may be important for liver adaptation to warmer temperatures.Support or Funding InformationFunded by NSF Grant IOS‐1355098.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Climate change and the northern elephant seal (Mirounga angustirostris) population in Baja California, Mexico.

The Earth′s climate is warming, especially in the mid- and high latitudes of the Northern Hemisphere. The northern elephant seal (Mirounga angustirostris) breeds and haul-outs on islands and the mainland of Baja California, Mexico, and California, U.S.A. At the beginning of the 21st century, numbers of elephant seals in California are increasing, but the status of Baja California populations is unknown, and some data suggest they may be decreasing. We hypothesize that the elephant seal population of Baja California is experiencing a decline because the animals are not migrating as far south due to warming sea and air temperatures. Here we assessed population trends of the Baja California population, and climate change in the region. The numbers of northern elephant seals in Baja California colonies have been decreasing since the 1990s, and both the surface waters off Baja California and the local air temperatures have warmed during the last three decades. We propose that declining population sizes may be attributable to decreased migration towards the southern portions of the range in response to the observed temperature increases. Further research is needed to confirm our hypothesis; however, if true, it would imply that elephant seal colonies of Baja California and California are not demographically isolated which would pose challenges to environmental and management policies between Mexico and the United States.

A new species of the genusAnelpistina(Insecta: Zygentoma: Nicoletiidae) from Todos Santos, Baja California Sur, Mexico

Abstract Anelpistina californica, new species (Insecta: Zygentoma: Nicoletiidae), from the Peninsula of Baja California, Mexico, is described. We report here the 16S rRNA sequence of this new species. The information in this study will be useful in future studies of nicoletiids from Baja California, especially those that use nicoletiids to calibrate molecular clocks. Baja California populations were separated from mainland continent populations in the late Miocene to Pliocene 13–5 mya when the Gulf of California appeared.

Phylogeography of Ramalina menziesii, a widely distributed lichen‐forming fungus in western North America

The complex topography and climate history of western North America offer a setting where lineage formation, accumulation and migration have led to elevated inter- and intraspecific biodiversity in many taxa. Here, we study Ramalina menziesii, an epiphytic lichenized fungus with a range encompassing major ecosystems from Baja California to Alaska to explore the predictions of two hypotheses: (i) that the widespread distribution of R. menziesii is due to a single migration episode from a single lineage and (ii) that the widespread distribution is due to the formation and persistence of multiple lineages structured throughout the species' range. To obtain evidence for these predictions, we first construct a phylogenetic tree and identify multiple lineages structured throughout the species' range--some ancient ones that are localized and other more recent lineages that are widely distributed. Second, we use an isolation with migration model to show that sets of ecoregion populations diverged from each other at different times, demonstrating the importance of historical and current barriers to gene flow. Third, we estimated migration rates among ecoregions and find that Baja California populations are relatively isolated, that inland California ecoregion populations do not send out emigrants and that migration out of California coastal and Pacific Northwest populations into inland California ecoregions is high. Such intraspecific geographical patterns of population persistence and dispersal both contribute to the wide range of this genetically diverse lichen fungus and provide insight into the evolutionary processes that enhance species diversity of the California Floristic Province.

Model‐based comparisons of phylogeographic scenarios resolve the intraspecific divergence of cactophilic Drosophila mojavensis

The cactophilic fly Drosophila mojavensis exhibits considerable intraspecific genetic structure across allopatric geographic regions and shows associations with different host cactus species across its range. The divergence between these populations has been studied for more than 60years, yet their exact historical relationships have not been resolved. We analysed sequence data from 15 intronic X-linked loci across populations from Baja California, mainland Sonora-Arizona and Mojave Desert regions under an isolation-with-migration model to assess multiple scenarios of divergence. We also compared the results with a pre-existing sequence data set of eight autosomal loci. We derived a population tree with Baja California placed at its base and link their isolation to Pleistocene climatic oscillations. Our estimates suggest the Baja California population diverged from an ancestral Mojave Desert/mainland Sonora-Arizona group around 230,000-270,000years ago, while the split between the Mojave Desert and mainland Sonora-Arizona populations occurred one glacial cycle later, 117,000-135,000years ago. Although we found these three populations to be effectively allopatric, model ranking could not rule out the possibility of a low level of gene flow between two of them. Finally, the Mojave Desert population showed a small effective population size, consistent with a historical population bottleneck. We show that model-based inference from multiple loci can provide accurate information on the historical relationships of closely related groups allowing us to set into historical context a classic system of incipient ecological speciation.

Taxonomy of Calyptridium parryi (Montiaceae)

Calyptridium parryi (Montiaceae, formerly Portulacaceae) putatively comprises four varieties: arizonicum, hesseae, nevadense, and parryi. We performed a detailed phenetic analysis of seed, fruit, and sepal morphology in order to assess the distinction and rank of these varieties. We treated the San Pedro Martir Mountains, Baja California populations of C. parryi as a separate taxonomic unit in these studies, given their great disjunct distribution. In addition, we included the very similar and largely sympatric C. monandrum in these analyses. Results from ANOVA and principal components analysis indicate that the six entities examined are, to various degrees, morphologically diagnosable. Calyptridium parryi varieties hesseae, nevadense, and parryi show some overlap in features, and we propose keeping these as varieties. Populations from the San Pedro Martir Mountains are distinct from other varieties of C. parryi, possibly warranting varietal status, but further studies with more samples are needed to confirm this. However, we conclude that C. parryi variety arizonicum is different enough in several features and geographic range to warrant species status, by a taxonomic/morphologic species concept. Calyptridium monandrum should be retained as a separate species.

Functional genomics of cactus host shifts in Drosophila mojavensis

Understanding the genetic basis of adaptation to novel environments remains one of the major challenges confronting evolutionary biologists. While newly developed genomic approaches hold considerable promise for addressing this overall question, the relevant tools have not often been available in the most ecologically interesting organisms. Our study organism, Drosophila mojavensis, is a cactophilic Sonoran Desert endemic utilizing four different cactus hosts across its geographical range. Its well-known ecology makes it an attractive system in which to study the evolution of gene expression during adaptation. As a cactophile, D. mojavensis oviposits in the necrotic tissues of cacti, therefore exposing larvae and even adults to the varied and toxic compounds of rotting cacti. We have developed a cDNA microarray of D. mojavensis to examine gene expression associated with cactus host use. Using a population from the Baja California population we examined gene expression differences of third instar larvae when reared in two chemically distinct cactus hosts, agria (Stenocereus gummosus, native host) vs. organpipe (Stenocereus thurberi, alternative host). We have observed differential gene expression associated with cactus host use in genes involved in metabolism and detoxification.

Phylogeography of Pseudacris regilla (Anura: Hylidae) in western North America, with a proposal for a new taxonomic rearrangement

The Baja California populations of Pseudacris regilla, a widespread species in Western North America ranging from British Columbia to southern Baja California, are characterized by extensive geographic fragmentation. We performed phylogeographic and historical demographic analyses on 609 bp of the cytochrome b mitochondrial gene of 110 individuals representing 28 populations to determine the relative influences of current and historical processes in shaping the present distribution of genetic diversity on the Baja California Peninsula. Haplotypes from this area were nested in a clade with three well-differentiated groups. Two of these groups are from Baja California Sur and another is from California and Baja California. The estimated date for the split of these groups, between 0.9–1 Ma, fits with previously proposed hypotheses of vicariance due to different transpeninsular seaways, although successive population fragmentation and expansion due to climatic oscillations during Pleistocene glaciations cannot be discarded. Historical demographic analyses detected signs of past population expansions, especially in the southernmost group. With respect to populations north of this region, two older clades were identified, one with haplotypes mainly distributed in central California, and the other corresponding to the northern half of the species range, in what apparently is a recurrent pattern in the Pacific coast of North America. Based on the concordance between mt-DNA and available allozyme data indicating that these species have a long independent evolutionary history, we propose to consider the three major clades as distinct species: P. regilla, P. pacifica, and P. hypochondriaca.

Epicuticular hydrocarbon variation in Drosophila mojavensis cluster species.

Epicuticular hydrocarbon variation was investigated among the three species of the Drosophila mojavensis cluster (D. mojavensis, D. arizonae, and D. navojoa) within the large D. repleta group. Because these hydrocarbons serve as contact pheromones in adult D. mojavensis, the chemical characteristics and differences in hydrocarbon profiles in populations of these three sibling species were further investigated. Twenty-seven hydrocarbon components with chain lengths ranging from C28 to C40, including n-alkanes, methyl-branched alkanes, n-alkenes, methyl-branched alkenes, and alkadienes were observed. Hydrocarbon profiles among the three species reared on different cactus hosts were easily aligned with previously identified components in D. mojavensis. Male and female D. navojoa possessed a 31-methyldotricont-6-ene absent in both D. arizonae and D. mojavensis, while lacking the 8,24-tritricontadiene present in these two species. D. navojoa adults had far less 2-methyloctacosane than these sibling species, but the significance of this difference was obscured by the degree of variation among populations in amounts of this hydrocarbon. Mainland and Baja California populations of D. mojavensis were fixed for differences in the amounts 8,24-tritricontadiene, 9,25-pentatricontadiene, and 9,27-heptatricontadiene, consistent with all previous studies. Amounts of 18 of the 27 hydrocarbon components were greater in flies reared on Opuntia cactus. Canonical discriminant function analysis resolved all three species into distinct, nonoverlapping groups, suggesting that epicuticular hydrocarbon profiles are species-specific in the D. mojavensis cluster. Based on the amounts of interpopulation variation in hydrocarbon profiles in these three species, we hypothesize that epicuticular hydrocarbon differences may evolve early during the formation of new species.

Premating Isolation Is Determined by Larval Rearing Substrates in CactophilicDrosophila mojavensis.IV. Correlated Responses in Behavioral Isolation to Artificial Selection on a Life‐History Trait

Studies of behavioral isolation among geographically isolated populations of Drosophila mojavensis have provided an understanding of incipient speciation wherein phylogeny and ecology play a prominent role. Populations of D. mojavensis in mainland Mexico and southern Arizona exhibit low but significant premating isolation from Baja California populations in laboratory mate choice tests. These same populations have undergone considerable life-history evolution in response to use of different host plants, suggesting that behavioral isolation between populations is a pleiotropic consequence of adaptation to different environments, or Mayr's geographic speciation hypothesis. This hypothesis was tested using bidirectional artificial selection on egg-to-adult development time in replicate lines of a mainland and Baja population cultured on two host cacti for 13 generations. Response to selection was greatest in the slow lines cultured on one host, yet there was uneven response in some lines due to variation in cactus tissue quality. Realized heritabilities for development time ranged from 0.04 to 0.16, which is consistent with previous estimates from half-sib/full-sib analyses of genetic variation. In most lines that responded to selection, premating isolation decreased to near zero. Correlated responses in behavioral isolation suggest that adaptation to contrasting environments can cause secondary responses in mate recognition systems that can influence the formation of new species.

Genetic differentiation and reproductive incompatibility among Baja California populations of the copepod Tigriopus californicus

Populations of the harpacticoid copepod Tigriopus californicus were sampled from five sites from San Diego, California, to Playa Altamira, Baja California, Mexico. Allozyme analyses revealed that all the study populations are sharply differentiated genetically. At the extreme, two populations, Punta Baja and Playa Altamira, have no alleles in common at the seven allozyme loci studied. All pairwise interpopulation crosses successfully produced F2 hybrids except those involving the Playa Altamira population. All crosses using Playa Altamira females failed to produce F1 hybrids, while Playa Altamira males successfully produced F1 progeny with females from all other sites. These F1 offspring, however, were completely sterile (with San Diego and Punta Banda females) or only occasionally produced F2 offspring (with Punta Morro and Punta Baja females). These results suggest that allopatric differentiation among Baja populations has resulted in exceptionally high levels of genetic divergence and nearly complete reproductive isolation of the Playa Altamira population, which should now be recognized at the semispecies (or perhaps sibling species) level.

Pre-mating isolation is determined by larval rearing substrates in cactophilicDrosophila mojavensis. II. Effects of larval substrates on time to copulation, mate choice and mating propensity

It has been hypothesized that reproductive character displacement has evolved in mainland Sonora, Mexico populations of cactophilicD. mojavensis due to the presence of a sympatric sibling speciesD. arizonae. In laboratory tests using ancestral Baja California populations and derived, sympatric mainland populations, asymmetrical sexual isolation has been observed among populations ofD. mojavensis where mainland females discriminate against Baja males. Effects of different pre-adult rearing environments on adult mating behaviour were assessed by comparing fermenting cactus tissues like those used in nature for breeding with laboratory media because previous studies have employed synthetic growth media for fly growth and development. Significant behavioural isolation was evident in all cases when larvae were reared on laboratory food, but was non-significant when flies were reared on fermenting cactus, except for the cactus used by most mainland populations, consistent with previous studies. Time to copulation of Baja females was greater than mainland females over all substrates, but male time to copulation did not differ between populations. Time to copulation for both sexes was significantly greater when flies were reared on laboratory food with one exception. The degree of behavioural isolation was weakly correlated with time to copulation across food types (Spearman rank correlation = 0.58,p = 0.099). Therefore, use of laboratory media in this and previous studies exaggerated adult pre-mating isolation and time to copulation in comparison to natural breeding substrates. These experiments suggest that a change in host substrates by saprophagous insects (where chemical differences exist between hosts) may have subtle effects on mating behaviour in a manner which promotes low levels of sexual isolation as a by-product of their utilization of a particular substrate during larval development. ForD. mojavensis, these results suggest that over evolutionary time, radiation into a new environment (from Baja to the mainland) allowed utilization of new host plants that may have incidentally promoted the sexual isolation patterns that have been observed within this species.

Spatial and temporal variation in recruitment of Aplysia californica Cooper: patterns, mechanisms and consequences

Recruitment of the sea hare, Aplysia californica Cooper, was examined at 10 rocky reefs off the coast of Santa Catalina Island, CA, for up to 3 yrs or more. A. californica recruit primarily to the red alga Plocamium cartilagineum Dixon. Recruitment intensity (number of recruits/kg Plocamium) differed dramatically but consistently between reefs, and varied between months. Recruitment during January—February probably consists of larvae spawned locally, in the Channel Islands area, during the summer peak in reproduction. Recruitment during June to September probably consists of larvae spawned in the Baja California, Mexico, region which are carried north by summer currents. Reproduction is cued by high temperatures in the summer, and occurs over a large range of body sizes. Winter thcruits that survive to the summer reproduce at masses of 500 g or more, while summer recruits reproduce the same season at masses of around 0.75 g. Survival of winter recruits is low, but survivors have high fecundity because of their large body size. Consequently, the average winter recruit has a greater expected fecundity than the average summer recruit. Summer recruits represent regular larval immigration from souther A. californica populations, and contribute a measurable amount to the yearly egg production at Santa Catalina Island. The asynchronous seasonal reproductive patterns of Channel Island and Baja California populations may be important to the population dynamics of these populations since they are linked by a common larval pool.

Variability in Island Populations of the House Finch

Abstract Coefficients of variation and generalized variances are compared for nine morphological characters from five mainland and four island populations of the House Finch (Carpodacus mexicanus). The purpose is to test the idea that variability is reduced in isolated populations and that there is a "population variation parameter" that determines the level of variation in most characters. Variability is greater in bill characters for Guadalupe and San Benito Islands than for mainland and other island populations. There are no consistent differences among samples in variability of wing, tail, or hind-limb characters, except for a tendency toward increased tarsus-length variability in a southern Baja California population and reduced variability in this character in San Clemente Island and Guadalupe Island populations. In bill characters, increased variability is found in the most divergent populations. The results do not support the generalization that geographic (= genetic) isolation per se causes much of a change in variability in island populations of birds, nor is there support for the idea of a pervasive quality of the gene pool that determines the level of variability in most characters.

Taxonomic and Biogeographic Relationships of Baja California Chickarees (Tamiasciurus)

Results of four statistical analyses consistently separated samples of Tamiasciurus from Baja California from samples of T. douglasii and T. hudsonicus. Univariate statistics indicated that 12 of 17 cranial characters were individually suffi- cient to distinguish one group from another. Discriminant analysis separated the two species and the Baja California group by equal intervals; distance coefficients among the three were similar. Individual populations within each group showed considerable overlap whereas the three groups did not overlap. Principal components analysis in- dicated that T. douglasii and T. hudsonicus differ primarily in size, whereas the Baja California group differs in shape from the other two species. Biogeographic evidence suggests that Tamiasciurus entered Baja California at one or more glacial maxima during the Pleistocene and a population was isolated by interglacial warming. The latest corridor would have closed about 15,000 years ago. Morphologic data indicate that the Baja California population warrants species status as T. mearnsi. The genus Tamiasciurus contains two species, T. douglasii and T. hudsonicus, and 29 subspecies (four in T. douglasii and 25 in T. hudsonicus; Hall and Kelson, 1959). The two species are distributed throughout most montane areas of North America with an area of contact in the Pacific Northwest. The distribution of each species is essentially continuous except for an isolated group in the Sierra San Pedro Martir of Baja California. The Baja California population, currently named T. douglasii mearnsi

Meiotic Drive in Natural Populations of Drosophila melanogaster. VI. A Preliminary Report on the Presence of Segregation-Distortion in a Baja California Population

The phenomenon of segregation-distortion, originally discovered in Madison, Wisconsin, has now been detected in a natural population of Drosophila melanogaster from Baja California. It has been demonstrated that the second chromosome responsible for the aberrant segregation is an SD-bearing chromosome, because it shares the following properties with the Madison SD: (1) It is expressed in the male sex only. (2) It is inhibited by the Curly inversion. (3) The Baja California SD chromosome is not sensitive to the action of the Madison SD chromosome. (4) It is located near the centromere (closely linked to cn). This finding suggests that SD is not of recent origin.