Sonoran Desert Region Research Articles

Differential seasonal prevalence of yellowing viruses infecting melon crops in southern California and Arizona determined by multiplex RT-PCR and RT-qPCR.

Viruses transmitted by the whitefly (Bemisia tabaci) are an increasing threat to cucurbit production in the southwestern United States as well as many other cucurbit production regions throughout the world. The crinivirus, cucurbit yellow stunting disorder virus (CYSDV), has severely impacted melon production in California and Arizona since its introduction to the region in 2006. Within the past few years, another crinivirus, cucurbit chlorotic yellows virus (CCYV), and the whitefly-transmitted ipomovirus, squash vein yellowing virus (SqVYV) were found infecting melon plants in California's Imperial Valley as well. Both CYSDV and CCYV, as well as an aphid transmitted polerovirus, cucurbit aphid-borne yellows virus (CABYV), occur together in the region and produce identical yellowing symptoms on cucurbit plants. Mixed infections of these four viruses both in the Sonoran Desert and other regions pose challenges for disease management and efforts to develop resistant varieties. A multiplex single-step RT-PCR method was developed that differentiates these viruses from one another, and this was used to determine the prevalence and distribution these viruses in melon samples collected from fields in the Sonoran Desert melon production region of California and Arizona, USA during spring and fall melon seasons from 2019 through 2021. TaqMan probes were also developed, optimized, and applied in a single-step multiplex RT-qPCR to quantify titers of these four viruses in plant samples, which frequently carry mixed infections. Results of the multiplex RT-PCR analysis demonstrated that CYSDV is the predominant virus during the fall season, whereas CCYV was by far the most prevalent virus during spring seasons each year. Multiplex RT-qPCR was used to evaluate differential accumulation and spatio-temporal distribution of viruses within plants and suggested differences in competitive accumulation of CCYV and CYSDV within melon. This study also provides the first official report of SqVYV in Arizona, USA, and offers an efficient method for virus detection and quantification for breeding and disease management in areas impacted by cucurbit yellowing viruses.

Haboob Dust Storms and Motor Vehicle Collision-related Trauma in Phoenix, Arizona.

The Sonoran Desert region, encompassing most of southern Arizona, has an extreme climate that is famous for dust storms known as haboobs. These storms lead to decreased visibility and potentially hazardous driving conditions. In this study we evaluate the relationship between haboob events and emergency department (ED) visits due to motor vehicle collisions (MVCs) in Phoenix, Arizona. This study is a retrospective analysis of MVC-related trauma presentations to Phoenix, AZ, hospitals before and following haboob dust storms. These events were identified from 2009-2017 primarily using Phoenix International Airport weather data. De-identified trauma data were obtained from the Arizona Department of Health Services (ADHS) Arizona State Trauma Registry (ASTR) from seven trauma centers within a 10-mile radius of the airport. We compared MVC-related trauma using six- and 24-hour windows before and following the onset of haboob events. There were 31,133 MVC-related trauma encounters included from 2009-2017 and 111 haboob events meeting meteorological criteria during that period. There was a 17% decrease in MVC-related ED encounters in the six hours following haboob onset compared to before onset (235 vs 283, P = 0.04), with proportionally more injuries among males (P < 0.001) and higher mortality (P = 0.02). There was no difference in frequency of presentations (P = 0.82), demographics, or outcomes among the 24-hour pre-and post-haboob groups. Haboob dust storms in Phoenix, Arizona, are associated with a decrease in MVC-related injuries during the six-hour period following storm onset, likely indicating the success of public safety messaging efforts. Males made up a higher proportion of those injured during the storms, suggesting a target for future interventions. Future public-targeted weather-safety initiatives should be accompanied more closely by monitoring and evaluation efforts to assess for effectiveness.

Seeds of Wisdom: Toward Healing a Cultural Divide

Seeds of Wisdom:Toward Healing a Cultural Divide Sarah Blomquist (bio) Sometimes the world will play with you, and that's how people get lost. — A Yaqui elder Click for larger view View full resolution Encased desert seeds harvested within southern Arizona: Purple speckled pods on the outer left, mesquite; light green pods on the outer right, mesquite; spiky footballs, cocklebur; red round wrinkled berries, manzanita; white fluffy seeds below manzanita, ocotillo; smallest dark brown paper seeds at bottom center, dock; lighter brown papery seeds to the right of dock, sotol; black center seeds, devil's claw; brown speckled pods above sotol, ironwood; light brown pods between spiky footballs and devil's claw, palo verde. Mark Blomquist, © 2021. Around the bend, past the lichen-encrusted boulders and magnificent desert views, I stopped at the patch of land where I envisioned harvesting food. The desert chia and saguaro were mostly as I remembered them, except now the saguaro was dripping with luscious, crimson fruits and [End Page 529] the desert chia was dried and papery, storing away tiny seeds that I intended to gather. As I have learned to do from my many teachers, I trod the earth lightly and collected sparingly, offering gratitude to the seeds and the plants as I disturbed their habitats. The stately saguaro cactus, Carnegiea gigantea, an iconic plant in the Sonoran Desert region, bears sweet fruits that have been a staple for the Tohono O'odham people for thousands of years. Desert chia, Salvia columbariae, likewise has served as food and medicine to the Indigenous peoples of the desert Southwest. Cactus fruit and mesquite flours have re-emerged as mainstream edible options, particularly in the regions where they are abundant. This is one among the many trends rekindling interest in and respect for the foods, medicines, and traditions rooted in the rich landscapes that contemporary humans now occupy. Collectively, we are standing at both an exciting and delicate crossroads in our relationship with foods, medicines, and land. Western technology and science are in their infancies when it comes to understanding the technologies and traditions of native peoples. Such technologies and traditions have often been stolen or not used respectfully by non-natives. However, people who have occupied these lands for millennia may still hold a wealth of knowledge and culture, if it has not been lost to processes of modernization. It is a difficult task to translate information and perspectives across these different cultural media, given the stark juxtaposition of the Click for larger view View full resolution Hands holding dried chia flowers with desert scrub in the background. Mark Blomquist, © 2021. [End Page 530] cultures, as well as the divide created by traumas past and present. As we apply our modern mindsets and tools to our ancestors' world and their relationship with the land, I wonder how we might collectively navigate this cultural mixture with more kindness, respect, and grace. Nutritional Science and Evolutionary Biology Back in the laboratory, I spent the day extracting fatty acids from the wide array of desert seeds I had harvested with care. A primary focus of the laboratory in which I conduct research is lipid biochemistry. Fatty acids are a type of lipid, where lipids represent one of the main macronutrient groups, which include carbohydrates and proteins. In this project, we are examining the nutritional profile and properties of foods of the ancestors who lived in the Sonoran Desert. As humans have evolved over many hundreds of thousands of years, they have adapted to their environments in order to survive. Multiple environmental conditions have shaped our current biology: the domestication of animals, differences in exposure to sunlight, exposure to bacteria (both symbiotic and pathogenic), and interactions with the dietary landscape. When compared to the deep historical past, for the last several hundred years of our development, in particular starting with industrialization, human beings have faced quite novel living conditions. While our bodies and biology remain more or less those of our ancestors, our modern environments are unique. Over the course of this history, most ancestral ways of being have been brutally extinguished or at least have deteriorated significantly due to modern forces. It is...

A Multivariate Study of Morphological Characters for Echinocactus horizonthalonius and E. texensis (Cactaceae) and Description of a New Subspecies, E. horizonthalonius subsp. australis

A study was conducted to ascertain the taxonomic validity of the endangered taxon Echinocactus horizonthalonius var. nicholii and whether there may be other groups of populations worthy of subspecies status within the range of the species. To test the hypothesis that individuals of E. horizonthalonius var. nicholii are morphologically distinct from those of the typical variety, a multivariate analysis was done to compare the degree of morphological variation or phenotypic plasticity of stem characters within populations to the variation among populations of E. horizonthalonius throughout its known range. Populations of E. texensis were sampled for outgroup comparison. Discriminant function analysis (DFA) assigning individuals by population showed loose groupings of geographically correlated populations. The DFA assigning individuals to regions or potential subspecific taxa indicated high percentages of correct classification for individuals within populations grouped into the Chihuahuan Desert, Sonoran Desert, and Central Mexican Plateau regions. Taxonomically, these groups correspond to E. horizonthalonius subsp. horizonthalonius (Chihuahuan Desert), E. horizonthalonius var. nicholii (Sonoran Desert), and unnamed taxon of E. horizonthalonius (Central Mexican Plateau). Because these morphological entities are correlated with regional distributions, they are placed here under subspecies, including a newly described taxon, E. horizonthalonius subsp. australis. Because no type for E. horizonthalonius could be located, a neotype is designated.

Remarkably rapid, recent diversification of Cochemiea and Mammillaria in the Baja California, Mexico region.

The Cactaceae of northwestern Mexico and the southwestern United States constitute a major component of the angiosperm biodiversity of the region. The Mammilloid clade, (Cactaceae, tribe Cacteae), composed of the genera Cochemiea, Coryphantha, Cumarinia, Mammillaria, and Pelecyphora is especially species rich. We sought to understand the timing, geographical and climate influences correlated with expansion of the Mammilloid clade, through the Sonoran Desert into Baja California. We reconstructed the historical biogeography of the Mammilloid clade, using Bayesian and maximum likelihood methods, based on a strongly supported molecular phylogeny. We also estimated divergence times, the timing of emergence of key characters, and diversification rates and rate shifts of the Mammilloid clade. We found that the most recent common ancestor of Cochemiea arrived in the Cape region of Baja California from the Sonoran Desert region approximately 5 million years ago, coinciding with the timing of peninsular rifting from the mainland, suggesting dispersal and vicariance as causes of species richness and endemism. The diversification rate for Cochemiea is estimated to be approximately 12 times that of the mean background diversification rate for angiosperms. Divergence time estimation shows that many of the extant taxa in Cochemiea and Baja California Mammillaria emerged from common ancestors 1 million to 200,000 years ago, having a mid-Pleistocene origin. Cochemiea and Mammillaria of the Baja California region are examples of recent, rapid diversification. Geological and climatic forces at multiple spatial and temporal scales are correlated with the western distributions of the Mammilloid clade.

Effects of Being in Contact with Nature on Individuals' Nature Connectedness: Excursion on the “Pinacate y Gran Desierto de Altar” Biosphere Reserve

Nature connectedness is often studied in relation to the interaction and contact with nature of individuals. In this study, we evaluate volunteers (n = 24) who conformed a group of excursionists in the Pinacate y Gran Desierto de Altar Biosphere Reserve (PGDABR), who are residents of Hermosillo (ages 18–62), in northwestern Mexico. The excursion consisted of a 2-day weekend visit to the Sonoran Desert region in which participants hiked, watched native species, stargazed, and enjoyed the crater's scenery, among other activities in nature. Volunteers were evaluated with an adapted 32-item questionnaire before and after their excursion. The instrument was comprising the Nature Connectedness (NC), Nature Relatedness, and Love and Care for Nature scales (LCNSs) to measure the sample level of feeling oneself as a part of nature and within it. This study aims to estimate if regions such as the Sonoran Desert, which presents extreme climate conditions, contribute to an enhancement on individuals' NC level. Findings indicate that participants displayed significant increasement levels on the NC and LCNSs after excursioning in PGDABR.

FORAGE YIELD, ELONGATION RATE AND BOTANICAL COMPOSITION OF Lolium multiflorum LAMB. IN RESPONSE TO DIFFERENT GRAZING INTERVALS AND INTEN

&lt;p&gt;&lt;strong&gt;Background.&lt;/strong&gt; The intensity and grazing interval are two very important factors in the management of grasslands that can affect the morphological and productive behavior of the forage species. Due to its productivity and persistence to grazing, ryegrass (&lt;em&gt;Lolium multiflorum&lt;/em&gt; Lamb.) is the main source of pasture for backgrounding cattle during winter-spring in northwestern México. Therefore, it is important to generate knowledge of established pasture with grasses to generate information that will serve producers to improve the economic profitability of livestock activities. &lt;strong&gt;Objective.&lt;/strong&gt; The objective of this study was to evaluate the influence of grazing intensity (GI) and grazing interval (GIv) on forage yield, elongation rate and botanical composition of ryegrass, under ambient conditions of this arid region. &lt;strong&gt;Hypothesis. &lt;/strong&gt;It is evident to observe that GIv and GI modify the forage yield, elongation rate and botanical composition of &lt;em&gt;L. multiflorum&lt;/em&gt; established in irrigated grassland in temperate climate zones.&lt;strong&gt; Methodology.&lt;/strong&gt; The study involved 1008 crossed bull calves (&lt;em&gt;Bos indicus &lt;/em&gt;ˣ&lt;em&gt; Bos taurus&lt;/em&gt;) of 16 months of age. Calves were distributed in a 3 ˣ 2 factorial arrangement in an RCB design, with three repetitions. Three GIv (21, 28 and 35-d) and two GI (grazed to 4 to 6 cm vs 10 to 12 cm) were evaluated. This 105-d trial was initiated on January 16, 2019, 90 days post-planting and finished on May 01, 2019, using an intensive grazing system with stocking rate of 56 calves per ha. The main effects of grazing interval were evaluated by means of orthogonal polynomials. &lt;strong&gt;Results.&lt;/strong&gt; Forage yield increased linearly (P&amp;lt;0.01) with increasing GIv; whereas with GIv of 28 and 35 days, yield increased with increased GI (interaction, P&amp;lt; 0.01). Stem contribution to yield increased linearly (P&amp;lt;.01) with increasing GIv. Forage lef to stem ratio decreased with increasing GIv and GI; however, at 28-d GIv, GI did not affect this ratio. &lt;strong&gt;Implications.&lt;/strong&gt; The results of the present study contribute to know the productive parameters of an established L.&lt;em&gt; multiflorum&lt;/em&gt; meadow in zones of arid climates under two intensities and three grazing intervals. &lt;strong&gt;Conclusions.&lt;/strong&gt; In conclusion, both grazing intensity and grazing interval are effective management tools to modify ryegrass performance during the hot ambient conditions of the Sonoran Desert region, associated with late-spring grazing period.&lt;/p&gt;

Release of tepary bean TARS‐Tep 23 germplasm with broad abiotic stress tolerance and rust and common bacterial blight resistance

AbstractTepary bean (Phaseolus acutifolius A. Gray) is a drought and high ambient temperature tolerant crop native to the Sonoran Desert, the hottest and driest region in the United States and Mexico. Although tepary bean is an orphan crop with little current commercial production, there was a brief period of larger scale production in the early 1900s in California. Tepary bean has great potential as a novel crop in a warmer world climate and can be introduced as an alternative pulse crop in hot and/or dry regions worldwide. TARS‐Tep 23 (Reg. no. GP‐309, PI 698457) is an improved tepary bean germplasm with wide‐ranging adaptation to tropical and temperate regions experiencing high temperature and drought stress conditions, with broad resistance to bean rust and with resistance to common bacterial blight. It has a flat, mottled black seed type with good seed size, a Type III plant habit, and a short crop cycle of 55–61 d in the environments tested. This germplasm was developed cooperatively by the USDA‐ARS, Zamorano University, the University of California–Davis, and the University of Nebraska. The use of this improved germplasm by farmers in production zones affected by abiotic and biotic stresses, or by breeding programs, can potentially increase seed yields of this climate‐resilient crop.

In memoriam Dr. Philip C. Rosen (1955-2020)

Philip Clark Rosen was born in New York City, USA, on February 25, 1955. “Phil” as he was known by many who knew him best, was a leading herpetologist and ecologist in the Sonoran desert region.

Notes on Stenochiini Kirby, 1837 genera and species from western North America (Coleoptera: Tenebrionidae)

The tribe Stenochiini Kirby, 1837 comprises six genera in North America with most species occurring in the tropical and temperateregions of the continent. Only two species in the genus Strongylium Kirby, 1818 have previously been reported from west of theContinental Divide in the United States from Arizona and New Mexico and no members of the tribe have been reported from the stateof Sonora, Mexico. We here report Strongylium tenuicolle (Say, 1826), known to be widely distributed east of the Rocky Mountains,from west of the Continental Divide for the first time from both Arizona and New Mexico. We similarly report the first records ofboth Strongylium apache Triplehorn and Spilman, 1973 and Strongylium atrum Champion, 1888 from Sonora. Oploptera chamelensis(Doyen, 1990) was previously known only from the type series from Jalisco, Mexico and is here reported from Sonora, which thereby extends the known range of this genus significantly. To promote consistency in generic recognition, we propose the transfer of Oploptera simplicicollis (LeConte, 1878) New Combination from Strongylium for the species distributed across the southeastern United States. Species diagnoses are given, and generic boundaries are discussed along with the expected diversity of the Sonoran Desert region.

Trends of daily extreme and non‐extreme rainfall indices and intercomparison with different gridded data sets over Mexico and the southern United States

AbstractTrends of 15 extreme and non‐extreme daily rainfall indices for Mexico and the southern United States are analyzed for the extended boreal winter (November–March) and summer (June–October) during 1981–2010. The analysis includes gridded observations (CHIRPS and Livneh), reanalyses (ERA5, ERA‐Interim, MERRA2, and CFSR), the regional climate model RegCM4.7 (forced by ERA‐Interim), and four general circulation models (GCMs) from the CMIP5 (HadGEM2‐ES, CNRM‐CM5, MPI‐ESM‐MR, and GFDL‐ESM2M). The domain is divided into 13 regions with similar seasonal rainfall patterns according to the k‐means algorithm applied to CHIRPS monthly precipitation, as a reference. Gridded observations and reanalyses (O&amp;R) show similar regional annual cycles and metrics of precipitation. The two observational data sets show the largest differences in the magnitude of some indices in the wettest region (southeastern Mexico) and in the monsoon. During summer, O&amp;R show positive significant trends in extreme rainfall indices in regions commonly affected by tropical cyclones (southern Baja California Peninsula, northeastern Mexico, and the southeastern United States), while negative significant trends of seasonal accumulation of rainfall are seen in the Mediterranean Californias and the Sonoran Desert region. There is an agreement among most data sets that the frequency and intensity of extreme winter precipitation indices have declined in northwest Mexico and the southwestern United States, but trends are not statistically significant, while southeastern Mexico shows significant increases in 5‐days accumulation (rx5d). ERA5 followed by MERRA2 show the best performance. RegCM4.7 reproduces the annual cycle of precipitation in most of the regions and captures the main trend signals especially in winter, but it has difficulties in reproducing the summer interannual variability of few indices. The GCMs tend to overestimate (underestimate) the annual cycle of precipitation and the median values of extreme indices in the driest (wettest) regions. They are not able to capture the regional trends of the indices.

Looking for the -scape in the sound: Discriminating soundscapes categories in the Sonoran Desert using indices and clustering

Soundscapes are increasingly used as innovative entry doors in environmental studies. Facing huge libraries of sound files which cannot be processed manually, acoustic indices provide an overview to the information contained in them, as well as to allow for automatic processing. Studies dealing with such indices have, however, focused more on specific topics or indices than on the overall characteristics of the soundscapes they were analyzing. The aim of this paper is to propose a holistic approach to soundscapes. Our hypothesis is that sufficient number and variety of indices can help frame the characteristics of sound environments and that the use of clustering algorithms allows us to group them in families and study the distribution of those across space and time, revealing a geography that will not necessarily coincide with the obvious landscape/visual geography. To demonstrate this point, we have run indices analysis and classification on a soundscapes database recorded in the Sonoran Desert region (Southeastern Arizona, USA). The results show that sound indices reveal temporal variations and patterns of soundscapes and point out to sometimes surprising similarities between otherwise different environments. As sound indices capture a wealth of information which characterizes the environment at a given place and time, they could be used as proxies to continuous monitoring without having to store extreme amounts of data.

A Microbiome Analysis of Soil Samples from Three Abandoned Lead-Silver Mines in the Arizona Sonoran Desert

There are many abandoned mines throughout the Arizona Sonoran Desert region and their environmental impact is yet to be fully understood. It was hypothesized that mining would result in decreased microbiome diversity, although some bacteria may adapt to the mine waste conditions. Soil samples were collected from three different mines in the Sonoran Desert and matched control sites. Soil total DNA was extracted and analyzed via 16S rRNA sequencing and analysis. Elemental analysis of the soils by x-ray fluorescence showed very different concentrations of toxic elements between the mine soils and the control sites. The concentrations of Pb, As, and Cu were as high as 8.1%, 0.72%, and 0.33%, respectively, of the soil mass at the mine soils, and thus much different than the control soils. There was an overall decrease in soil microbiome diversity and species richness in mine samples. Overall, approximately 50% of assigned Operational Taxonomic Units (OTU) overlapped between mine and control soil samples. Additionally, a total of 12 OTUs were detected within all mine soil samples and none of the control soil samples, suggesting these bacteria do not naturally occur in undisturbed desert soils within this region and instead were able to adapt to the extreme conditions of the former mines. One of these 12 bacteria was found to be a previously undescribed species that appears to be closely related to the phylum Chloroflexi.

Hot Spots and Hot Moments for On-Plant Foraging by Ants Within the Flora of Warm North American Deserts

Diagnosing the variability in prospective inter-specific interactions informs both our understanding of particular species as well as how the ecological complex of which they can be a part are altered by their presence. This study uses empirical field descriptions, complemented by published floras and the resources at centers for species conservation, to explore macro-ecological patterns in interactions between plants and ants. I describe on-plant foraging by ants on 70 plant species (11 families, 29 genera) in the Sonoran Desert region, highlighting particular combinations of plant species, ontogenetic stages, and season where forager visitation is disproportionately high or low. Through my plant-ant association surveys, I find species-specific descriptions of on-plant foraging: (1) are qualitatively similar among sites (an arboretum and a wilder location), (2) can predict the activities of ground foraging ants at the patch scale (plant neighborhoods of 12 m2), (3) show plant community types within the warm North American deserts have diverging likelihoods of on-plant foraging, and (4) brief inspections can describe among-plant variation in likelihoods of visitation by ants as well as herbivores that can be deterred by ants.

Ecology of the Western Queen Butterfly Danaus gilippus thersippus (Lepidoptera: Nymphalidae) in the Mojave and Sonoran Deserts.

The purpose of this study was to assess the ecological knowledge surrounding the western queen butterfly, Danaus gilippus thersippus (H. Bates). Specifically, our objectives were to synthesize existing data and knowledge on the ecology of the queen and use results of this assessment to inform the direction of future research on this understudied species. We identified six core areas for assessment: distribution, the biodiversity of plant resources, western queen and their host plant phenology, chemical ecology, and four key life history traits. We mapped the distribution of D. g. thersippus from museum specimen records, citizen science (e.g., iNaturalist) and image sharing app-based observations, along with other observational data enumerating all current known plant resources and long-range movements. We assembled 14 larval food plants, six pyrrolizidine alkaloids plants and six nectar plants distributed in the western Mojave and Sonoran Desert regions of the United States and Baja California. We report on its phenology and its long-range movement. Butterfly species have declined across the western US, and western monarch populations have declined by 97%. Danaus g. thersippus has received little research attention compared with its famous congener D. plexippus L. Danaus g. thersippus’ desert distribution may be at its temperature limits for the species distribution and for its rare host plant Asclepias nyctaginifolia.

The Tradition of Recycling Identity in Native Culture: The Re-Traditioning of Tradition

Our tribe is Yaqui, or Yoeme, or Hiaki Yoeme. Our traditional language is known as Yoemem; it is connected to the Uto-Aztecan language families that encompasses, among others, the O’odham, Tarahumara, Pima, Mayo and Huichol peoples of the Sonoran Desert regions of North and Central America. There are songs and dances that are shared between some of these language families that frequently contain images of the natural world, such as moths, flowers, deer, or mountains – elements that evoke connection in order to encourage the restoration of wellness and healing through telling stories of cycles of life. For our tribe, these are the songs and dances that one hears most often at ceremony. Repeating and rhythmic, growing up from the landscape, these songs and dances are the ones that call us home.

Relationships among climate, stem growth, and biomass δ13C in the giant saguaro cactus (Carnegiea gigantea)

AbstractGiant saguaro (Carnegiea gigantea) is one of the longest‐lived and massive cacti species in the Americas. They occur throughout the Sonoran Desert region with a distribution spanning a five‐fold gradient in mean annual precipitation. Relationships between fitness traits, including stem growth, and spatio‐temporal climate patterns are still poorly understood in saguaro, but are assumed to be largely coupled to summer precipitation. To better understand patterns of climate sensitivity in giant saguaro, annual stem growth, carbon isotope ratios (δ13C) in spine tissues, and seasonal variation in stem volume, a proxy for stem water storage, were evaluated over a single growing season (2014) in six widely distributed populations in the northern Sonoran Desert, and over four consecutive growing seasons (2013–2016) in two populations with differences in mean annual precipitation and site moisture (Mi), defined as precipitation amount divided by mean atmospheric vapor pressure deficit. We hypothesized that saguaro growth and δ13C would be coupled to a complex suite of climate conditions that include winter precipitation and aridity. Annual stem growth of all populations was generally better correlated to Mi than precipitation alone and was best correlated with Mi measured over the hydrologic year, October 2013–September 2014 (F = 39.8, P &lt; 0.0001). Likewise, mean δ13C increased with Mi, with the highest correlation with Mi calculated for July 2013–August 2014 (F = 38.4.0, P &lt; 0.0001). Annual stem growth measured across all populations was well correlated to δ13C in spines produced during the current year of growth (F = 36.3, P &lt; 0.0001). Annual variation in stem growth appeared to reflect annual variation in mean stem volume measured monthly from the summer of the previous year to the summer of the current year of growth. Results suggest that stem growth and photosynthetic physiology recorded by δ13C are coupled to a complex suite of climate conditions with a strong legacy effect from the previous summer and winter. These findings provide new insight on the effects of summer and winter drought and a warming climate on the photosynthesis, growth, and fitness of giant saguaro.

Molecular phylogeny, ecology and multispecies aggregation behaviour of bombardier beetles in Arizona.

Aggregations of conspecific animals are common and have been documented in most phyla. Multispecies aggregations are less common and less well studied. Eight species of Brachinus beetles —famous for their unique, highly effective, chemical defense—regularly settle together form large diurnal multispecies aggregations in dark, moist areas in riparian habitats in the Sonoran Desert Region. Here, we document these multispecies aggregations and investigate the incidence and dynamics of aggregation behavior. Analysis of species composition of 59 field-collected aggregations revealed that 71% contained more than one species, eight species regularly co-occurred in aggregations, and no two species showed a preference to aggregate with one another. We provide the first phylogenetic analyses of participants in multispecies aggregations, and find that Brachinus species found together in aggregations are not each other’s closest relatives but rather are dispersed throughout the phylogeny of the genus. Further, we find no tendency for species to aggregate with close relatives more frequently than distant relatives. Laboratory experiments on B. elongatulus showed that it chose to settle in occupied shelters over empty shelters. Experiments with B. hirsutus and B. elongatulus showed that B. hirsutus prefers to settle under shelters housing heterospecifics over conspecifics. Our findings suggest that these multispecies aggregations do not form by chance, but rather are initiated by a genus-wide aggregation cue associated with the presence of individuals already in a shelter, which is likely to be chemical and potentially tactile in nature.

Reproductive Output and Clutch Phenology of Female Agassiz's Desert Tortoises (Gopherus agassizii) in the Sonoran Desert Region of Joshua Tree National Park

Agassiz's desert tortoise (Gopherus agassizii) reaches the southern edge of its range in the Sonoran Desert of California. The reproductive ecology of this wideranging species is understudied here compared to populations in the adjacent Mojave Desert. Understanding potential geographic variation in reproductive ecology is important for effective management of conservation-reliant species like G. agassizii. We studied the fecundity and clutch phenology of female G. agassizii at two study sites in the Sonoran Desert region of Joshua Tree National Park over five years (1997–1999, 2015–2016) spanning two of the strongest El Nino events on record and an epic drought. Across all years, mean clutch size was 4.3±1.5 eggs, mean clutch frequency was 1.78 clutches/female/year, and mean X-ray egg width was 36.51±1.56 mm, all of which are comparable to other published studies both in the Sonoran and Mojave deserts of California. Our results generally support earlier published findings that G. agassizii utilize a bet-hedging strategy of consistently producing small clutches almost every year, even during times of low annual primary productivity. A regionally warmer climate in the Sonoran Desert of California appears to have an effect on the timing of egg production, as the earliest dates of egg visibility in our study (April 6) were approximately two weeks earlier than the earliest dates reported for G. agassizii in the Mojave Desert. Shelled eggs were no longer visible in tortoises after mid-June in all years but the El Nino year 1998, when eggs were visible until mid-July.

Temperature and Heat-Related Mortality Trends in the Sonoran and Mojave Desert Region

Extreme temperatures and heat wave trends in five cities within the Sonoran Desert region (e.g., Tucson and Phoenix, Arizona, in the United States and Ciudad Obregon and San Luis Rio Colorado, Sonora; and Mexicali, Baja California, in Mexico) and one city within the Mojave Desert region (e.g., Las Vegas, Nevada) were assessed using field data collected from 1950 to 2014. Instead of being selected by watershed, the cities were selected because they are part of the same arid climatic region. The data were analyzed for maximum temperature increases and the trends were confirmed statistically using Spearman’s nonparametric test. Temperature trends were correlated with the mortality information related with extreme heat events in the region. The results showed a clear trend of increasing maximum temperatures during the months of June, July, and August for five of the six cities and statically confirmed using Spearman’s rho values. Las Vegas was the only city where the temperature increase was not confirmed using Spearman’s test, probably because it is geographically located outside of the Sonoran Desert or because of its proximity to the Hoover Dam. The relationship between mortality and temperature was analyzed for the cities of Mexicali, Mexico and Phoenix. Arizona.