Variation in allozymes and stomatal size in pinyon (Pinus edulis, Pinaceae), associated with soil moisture

Microgeographic allozyme variation was examined in pinyon pine, Pinus edulis, among five collection sites in Owl Canyon, Colorado. Relatively dry and moist sites were identified by associated plant communities and the sizes and densities of trees. Three moist sites and two dry sites were compared, and because all sites were within 600 m of one another, isolation by distance was not considered as a viable explanation of genetic differentiation between sites. Allelic frequencies at glycerate dehydrogenase (Gly) differed by 14% between moist and dry areas, and the pattern of microgeographic variation found here-allele 3 higher in frequency on dry sites-was consistent with previous studies of microgeographic variation in contrasting moist and dry sites. Trees within one of the dry sites were examined to test the hypothesis that stomata sizes and densities are heterogeneous among Gly genotypes. Heterozygotes had the longest and widest stomata; the stomatal area of heterozygotes was 28% greater than the stomatal area of homozygotes. Whereas the stomatal areas of the two homozygotes were similar, their shapes did not overlap when projected on a bivariate plot of length and width. These results suggest that stomatal shape may play a role in adapting pinyon to heterogeneity in soil moisture.     

Herbivore deme formation on individual trees: a test case

We examined the deme-formation hypothesis, which states that sessile herbivores on long-lived hosts become locally adapted to the defensive phenotypes of individual trees. We showed a five-fold increase in resistance by individual pinyon pines (Pinus edulis) to the pinyon pine needle scale (Matsucoccus acalyptus). Although such variation could represent a significant selection pressure favoring deme formation, two lines of evidence led to rejection of the hypothesis. First, there were no significant differences in mortality among scale populations in a reciprocal transfer experiment. Second, a seven-year experiment showed that mortality of newly founded, incipient scale populations was similar to established scale populations. While our experiments fail to support the deme-formation hypothesis, they do demonstrate significant variation in the resistance traits of a natural tree population. Although we feel that demeformation is still probable in this system, it is likely to occur on a larger geographic scale than individual trees as proposed by Edmunds and Alstad.     

Relative Importance of Environmental Stress and Herbivory in Reducing Litter Fall in a Semiarid Woodland

We examined the impact of soil stress (low water and nutrient availabilities) and two keystone insect herbivores on pinyon pine (Pinus edulis) needle litterfall. We compared trees growing on two distinct soil types: volcanic cinders, which exhibit pronounced water and nutrient limitation, and sandy-loam soils, which have higher water-storage capacity and nutrient availability. Using two long-term herbivore removal experiments (15 and 18 years, respectively), we also examined the effects of the pinyon needle scale (Matsucoccus acalyptus, which attacks juvenile trees) and the stem-boring moth (Dioryctria albovittella, which attacks mature trees) on pinyon litterfall. These herbivores reach high densities on cinder soils but are absent or occur at much lower levels on sandy-loam soils. Four years of litterfall measurements showed four major patterns. First, independent of herbivory, needle litterfall was 20% lower under trees on high-stress cinder soils than on sandy-loam soils. Second, in agreement with the negative impact of scales on tree growth (that is, a 30% decline in stem growth), trees with scale infestations had 25% lower litterfall rates than trees resistant to scale; however, 15 years of scale-insect removal did not significantly increase needle litterfall. This implies possible intrinsic differences in litter production between scale-resistant and scale-susceptible trees. Third, in contrast with significant negative effects of moth herbivory on tree growth (that is, a 27% decline in stem growth), moth herbivory had no effect on needle litterfall. This, along with increased stem density in moth-susceptible trees, may be evidence of compensatory production. Fourth, there were strong year by soil type and year by scale herbivory interactions, such that in some years the effect on litterfall can be obscured or reversed by some other factor. In summary, soil stress has a strong and predictable effect on needle litterfall, whereas the relationship between insect herbivory and needle litterfall is weaker and depends on the individual herbivore. These effects, however, are mediated by other environmental factors that have considerable annual variation.     

Vicariance and dispersal in the differentiation of vocalization in the Ryukyu Scops Owl Otus elegans

The distribution of species and species diversity can be affected by vicariance or dispersal. To understand their role in shaping species distribution and population structure these two processes must be estimated within and among populations. I analysed large‐scale variation in the call structure of the Ryukyu Scops Owl Otus elegans. This owl is distributed over a 1200‐km range, and only inhabits islands. Within this range, I studied this species across 22 continental islands of the Ryukyu Archipelago and two oceanic islands. The study aimed to assess whether there is variation in the acoustic structure of Owl hoot calls within islands, among major groups of islands and across a large area comprising a major biogeographical barrier (the Kerama Gap). The acoustic structure of calls was homogeneous within islands and among major island‐groups. Acoustic differentiation, however, increased over longer geographical distances of up to about 1200 km. The acoustic structure of hoots of the Ryukyu Scops Owl populations was clearly divided into two groups, north and south of the Kerama Gap. It is suggested that the Kerama Gap acted as a biogeographical barrier and contributed to the differentiation between the two major island‐groups. It is likely that this difference developed during the fragmentation of a widespread ancestral population by vicariant isolating events. There was also evidence of an effect of dispersal on vocal differentiation in subspecies inhabiting the two oceanic islands.     

The pattern and range of movement of a checkered beetle predator relative to its bark beetle prey

Theoretical studies of predator‐prey population dynamics have increasingly centered on the role of space and the movement of organisms. Yet, empirical studies have been slow to follow suit. Herein, we quantified the long‐range movement of a checkered beetle, Thanasimus dubius, which is an important predator of a pernicious forest pest, the southern pine beetle, Dendroctonus frontalis. Adult checkered beetles were marked and released at five sites and subsequently recaptured at traps baited with pine and pine beetle semiochemicals and located at distances up to 2 km away from the release point. While the pattern of recaptures‐with‐distance at each site provided a modest fit to a simple random‐diffusion model, there was a consistent discrepancy between observed and expected recaptures: a higher than expected proportion of beetles were recaptured at the more distant traps. To account for this deviation, we developed a model of diffusion that allowed for simple heterogeneity in the population of marked beetles; i.e., a slow and fast moving form of the checkered beetle. This model provided a significantly better fit to the data and formed the basis for our estimates of intra‐forest movement. We estimated that on average, one half of the checkered beetles dispersed at least 1.25 km, one third dispersed>2 km, and 5% dispersed>5 km. The source of the heterogeneous dispersal rates were partially due to differences in beetle size: smaller beetles (for both males and females) were more likely to be recaptured away from the release site than larger beetles. The southern pine beetle (prey for the checkered beetle) exhibited no significant heterogeneity in dispersal ability and provided a very good fit to the simple diffusion model. The only difference in dispersal between these two species was that checkered beetles were undergoing greater long‐distance dispersal than the pine beetles (the radius containing 95% of the dispersing individuals was 5.1 km for the checkered beetle and 2.3 km for the pine beetle). Data on the movement of these two species is used to evaluate a general model of spatial pattern formation in a homogeneous environment, and the potential of the checkered beetle as a biological control agent for the southern pine beetle.     

The benefits of interpopulation hybridization diminish with increasing divergence of small populations

Interpopulation hybridization can increase the viability of small populations suffering from inbreeding and genetic drift, but it can also result in outbreeding depression. The outcome of hybridization can depend on various factors, including the level of genetic divergence between the populations, and the number of source populations. Furthermore, the effects of hybridization can change between generations following the hybridization. We studied the effects of population divergence (low vs. high level of divergence) and the number of source populations (two vs. four source populations) on the viability of hybrid populations using experimental Drosophila littoralis populations. Population viability was measured for seven generations after hybridization as proportion of populations facing extinction and as per capita offspring production. Hybrid populations established at the low level of population divergence were more viable than the inbred source populations and had higher offspring production than the large control population. The positive effects of hybridization lasted for the seven generations. In contrast, at the high level of divergence, the viability of the hybrid populations was not significantly different from the inbred source populations, and offspring production in the hybrid populations was lower than in the large control population. The number of source populations did not have a significant effect at either low or high level of population divergence. The study shows that the benefits of interpopulation hybridization may decrease with increasing divergence of the populations, even when the populations share identical environmental conditions. We discuss the possible genetic mechanisms explaining the results and address the implications for conservation of populations.     

Genetic signatures of translocations and habitat fragmentation for two evolutionarily significant units of a protected fish species

Genetic population structure was evaluated for the White Sands pupfish (Cyprinodon tularosa), a protected fish species comprised of two Evolutionarily Significant Units (ESUs); the Malpais Spring ESU and the Salt Creek ESU. The Malpais Spring ESU is restricted to Malpais Spring, whereas the Salt Creek ESU includes the native Salt Creek population and two Salt Creek-derived populations at Mound Spring and Lost River; all three of these habitats are physically fragmented. We sampled the upper and lower reaches of the four populations, examining 13 DNA microsatellite loci from 40 individuals per population. As expected, significant genetic structure was observed between the two ESUs; Malpais Spring and Salt Creek. Substantial genetic drift was observed for the introduced Lost River population, with modest genetic drift for the introduced Mound Spring population. Taken together with ecological data, neither of the introduced populations successfully replicates the Salt Creek population. We also report significant reductions in genetic diversity for the upper reaches of both Salt Creek and Lost River, indicating that recent habitat changes have altered the genetic structure of these two populations. We consider these findings along with previously reported ecological data to develop guidelines for managing C. tularosa.     

Deadly combination of genes and drought: increased mortality of herbivore-resistant trees in a foundation species

Current climate models predict a shift to warmer, drier conditions in the southwestern US. While major shifts in plant distribution are expected to follow these climate changes, interactions among species and intraspecific genetic variation rarely have been incorporated into models of future plant distributions. We examined the drought‐related mortality of pinyon pine (Pinus edulis) in northern Arizona focusing on trees that showed genetically‐based resistance or susceptibility to a nonlethal herbivore, the shoot‐boring moth, Dioryctria albovittella. Because moth resistant trees have outperformed susceptible trees during 20 years of study, and herbivory has been shown to increase drought related mortality, we expected higher mortality rates in susceptible trees. However, our field observations and greenhouse experiments showed several unexpected patterns relevant to understanding the consequences of climate change: (1) The mortality of adult P. edulis resistant to the moth was three times higher than the mortality of trees susceptible to the moth. (2) Over a few years, differential mortality caused a shift in stand structure from resistant dominated to equality (3 : 1 resistant : susceptible to 1 : 1). (3) Adult moth resistant trees suffered significantly greater water stress than adult moth susceptible trees, suggesting that variation among the two groups in drought tolerance may be a mechanism for differential mortality. (4) When grown under drought conditions in the greenhouse, seedlings from resistant mothers died sooner than seedlings from susceptible mothers. These data support the hypothesis that drought can act as an agent of balancing selection and that drought resistance is a heritable trait. Taken together, our findings suggest that genetic variation in a population can be an important factor in determining its response to future climate change, and argue for the inclusion of genetics into models developed to understand the consequences of climate change.     

Wide-range dispersal in juvenile Eagle Owls (Bubo bubo) across the European Alps calls for transnational conservation programmes

Although juvenile dispersal is an important life history component, it remains one of the less understood ecological processes regulating the dynamics of animal populations. Lack of information about patterns of dispersal hampers the estimation of the actual status and demographic trajectory of populations, and can preclude the development of sound conservation strategies. The Eagle Owl Bubo bubo is an endangered bird species in the European Alps. Many breeding sites have been abandoned in the twentieth century, although some recovery has been reported lately. Moreover, the occupancy of traditional breeding sites across years in well-monitored Alpine populations varies a lot, this despite a relatively high breeding success at the population level. This raises concern about the long-term persistence of Alpine populations. Using conventional and satellite radiotracking, we investigated the spatio-temporal dispersal of 41 juvenile Eagle Owls originating from a population in the southwestern Swiss Alps. Our main goal was to determine dispersal distances, places and times of post-dispersal settlement. Juveniles left their parents between mid-August and mid-November. They covered, on average, 12.7 km per night (linear distance between two consecutive day roosts), often crossing high mountain ranges (up to 3,000 m altitude). The mean total distance covered by an individual during dispersal was 102 km (sum of night movements), with a maximum of 230 km. Settlement places were, on average, 46 km distant from the birth place. Our study establishes long-distance dispersal in juvenile Eagle Owls, even in a complex topography, suggesting the existence of a wide-scale metapopulation system across the northwestern Alps. This metapopulation dimension should be accounted for in conservation plans.     

Using population viability analysis,genomics, and habitat suitability to forecast future population patterns of Little Owl Athene noctua across Europe

The agricultural scene has changed over the past decades, resulting in a declining population trend in many species. It is therefore important to determine the factors that the individual species depend on in order to understand their decline. The landscape changes have also resulted in habitat fragmentation, turning once continuous populations into metapopulations. It is thus increasingly important to estimate both the number of individuals it takes to create a genetically viable population and the population trend. Here, population viability analysis and habitat suitability modeling were used to estimate population viability and future prospects across Europe of the Little Owl Athene noctua, a widespread species associated with agricultural landscapes. The results show a high risk of population declines over the coming 100 years, especially toward the north of Europe, whereas populations toward the southeastern part of Europe have a greater probability of persistence. In order to be considered genetically viable, individual populations must count 1,000–30,000 individuals. As Little Owl populations of several countries count <30,000, and many isolated populations in northern Europe count <1,000 individuals, management actions resulting in exchange of individuals between populations or even countries are probably necessary to prevent losing <1% genetic diversity over a 100‐year period. At a continental scale, a habitat suitability analysis suggested Little Owl to be affected positively by increasing temperatures and urban areas, whereas an increased tree cover, an increasing annual rainfall, grassland, and sparsely vegetated areas affect the presence of the owl negatively. However, the low predictive power of the habitat suitability model suggests that habitat suitability might be better explained at a smaller scale.     

Long-distance colonization,isolation by distance,and historical demography in a relictual Mexican pinyon pine (Pinus nelsonii Shaw) as revealed by paternally inherited genetic markers (cpSSRs)

Pinus nelsonii is a relictual pinyon pine distributed across a wide altitudinal range in semiarid zones in Mexico near the border between the States of Nuevo León and Tamaulipas. It also occurs in small patches in the State of San Luis Potosí. Pinus nelsonii is classified in the monotypic subsection Nelsoniae, separated from other pinyon pines (subsection Cembroides), because it possesses several distinctive characters including persistent fascicle sheaths, connate needles, and a distinctive wood anatomy. In the present study, chloroplast simple sequence repeats (cpSSRs) were used to estimate genetic variation in most known populations (nine) of P. nelsonii. The genetic variation (HT = 0.73; 27 haplotypes in 256 individuals) is moderate when compared to other pine species. Population differentiation ranged between low and moderate (FST = 0.13 and RST = 0.05), as did the Nei and Goldstein genetic distances between populations. However, this pattern varied depending on whether the infinite alleles or stepwise mutation model was used. In the former case a significant isolation by distance was found, but not in the latter. A significant association between geographical and genetic structure in one clade, through a nested clade analysis, was found, which suggested long-distance colonization between 125000 and 309000 years ago. We found weak evidence for a population expansion. A mismatch distribution suggests that P. nelsonii populations underwent an expansion 4.25 times their size between 59000 and 146000 years ago. On the other hand, the populations' star-like phylogeny and a slight parabolic relationship between coalescence times and lineage number also suggest weak population expansion. Overall, this species appears to have been in demographic stasis for a large proportion of the time detected by the markers used.     

Does Seed‐Caching Experience Affect Spatial Memory Performance by Pinyon Jays?

Food‐storing birds use spatial memory to find previously cached food items. Throughout winter, pinyon jays (Gymnorhinus cyanocephalus) rely heavily on cached pinyon pine (Pinus edulis) seeds. Because of a recent severe drought, pinyon pine trees had not produced a significant seed crop for several years. Therefore, 1‐ and 2‐yr‐old birds never had the opportunity to cache and recover seeds and birds 4 or more years of age had not recovered seeds in 3 yr. This study examined whether natural but extreme variability in experience might result in differences in abstract spatial memory ability during a non‐cache recovery test of spatial memory. Three groups of jays were tested for spatial memory ability in an open room analog of the radial arm maze. Two of the groups were 8 mo old: young/minimally experienced birds which had 2 mo of experience in the wild, while young/experienced birds had 5 mo of experience in their natural habitat. The third group, adult, consisted of birds more than 3 yr old, with at least 3 yr of experience in their natural habitat. This was the only group with experience caching pine seeds. All three groups performed equally and well above chance. This suggests that spatial memory is fully developed by 8 mo of age and is not affected by extensive experience in the wild.     

GENETIC DIFFERENTIATION AND HETEROZYGOSITY IN PINYON PINE ASSOCIATED WITH RESISTANCE TO HERBIVORY AND ENVIRONMENTAL STRESS

Arizona's Sunset Crater began erupting in 1064 AD and for the next 200 years buried over 2,000 km² in ash, cinders, and lava. Soil analyses indicate that pinyon pines (Pinus edulis) currently colonizing the cinder fields are faced with a highly stressful environment. Many of these pinyons suffer chronic, intense insect herbivory that reduces plant growth and eliminates female cone production. In contrast, herbivory among pinyons growing in neighboring sandy-loam soils is minimal. Furthermore, numerous trees within the heavily infested cinder field population suffer relatively low herbivory and maintain normal growth and reproduction. We used four polymorphic enzymes to examine the relationship between herbivore attack, environmental stress and genotypes of the adjacent cinder field, and sandy-loam soil pinyon populations. Our results demonstrate that 1) resistant trees display significant genetic differences and are more heterozygous for two enzymes associated with herbivory than susceptible trees; and 2) the cinder-soil pinyons exhibit significant genetic differences and are more heterozygous for an enzyme associated with environmental stress than the neighboring sandy-loam soil pinyons. We conclude that heterozygosity of specific or closely linked loci may facilitate pinyon resistance to herbivory and environmental stress, and that strong selection across narrow geographic boundaries resulted in rapid genetic differentiation of pinyon populations.     

Neighboring trees affect ectomycorrhizal fungal community composition in a woodland-forest ecotone

Ectomycorrhizal fungi (EMF) are frequently species rich and functionally diverse; yet, our knowledge of the environmental factors that influence local EMF diversity and species composition remains poor. In particular, little is known about the influence of neighboring plants on EMF community structure. We tested the hypothesis that the EMF of plants with heterospecific neighbors would differ in species richness and community composition from the EMF of plants with conspecific neighbors. We conducted our study at the ecotone between pinyon (Pinus edulis)-juniper (Juniperus monosperma) woodland and ponderosa pine (Pinus ponderosa) forest in northern Arizona, USA where the dominant trees formed associations with either EMF (P. edulis and P. ponderosa) or arbuscular mycorrhizal fungi (AMF; J. monosperma). We also compared the EMF communities of pinyon and ponderosa pines where their rhizospheres overlapped. The EMF community composition, but not species richness of pinyon pines was significantly influenced by neighboring AM juniper, but not by neighboring EM ponderosa pine. Ponderosa pine EMF communities were different in species composition when growing in association with pinyon pine than when growing in association with a conspecific. The EMF communities of pinyon and ponderosa pines were similar where their rhizospheres overlapped consisting of primarily the same species in similar relative abundance. Our findings suggest that neighboring tree species identity shaped EMF community structure, but that these effects were specific to host-neighbor combinations. The overlap in community composition between pinyon pine and ponderosa pine suggests that these tree species may serve as reservoirs of EMF inoculum for one another.     

Landscape level analysis of mountain pine beetle in British Columbia, Canada: spatiotemporal development and spatial synchrony within the present outbreak

Eruptive herbivores can exert profound landscape level influences. For example, the ongoing mountain pine beetle outbreak in British Columbia, Canada, has resulted in mortality of mature lodgepole pine over >7 million ha. Analysis of the spatio‐temporal pattern of spread can lend insights into the processes initiating and/or sustaining such phenomena. We present a landscape level analysis of the development of the current outbreak. Aerial survey assessments of tree mortality, projected onto discrete 12×12 km cells, were used as a proxy for insect population density. We examined whether the outbreak potentially originated from an epicenter and spread, or whether multiple localized populations erupted simultaneously at spatially disjunct locations. An aspatial cluster analysis of time series from 1990 to 2003 revealed four distinct time series patterns. Each time series demonstrated a general progression of increasing mountain pine beetle populations. Plotting the geographical locations of each temporal pattern revealed that the outbreak occurred first in an area of west‐central British Columbia, and then in an area to the east. The plot further revealed many localized infestations erupted in geographically disjunct areas, especially in the southern portion of the province. Autologistic regression analyses indicated a significant, positive association between areas where the outbreak first occurred and conservation lands. For example, the delineated area of west‐central British Columbia is comprised of three conservation parks and adjacent working forest. We further examined how population synchrony declines with distance at different population levels. Examination of the spatial dependence of temporal synchrony in population fluctuations during early, incipient years (i.e. 1990–1996) suggested that outbreaking mountain pine beetle populations are largely independent at scales >200 km during non‐epidemic periods. However, during epidemic years (i.e. 1999–2003), populations were clearly synchronous across the entire province, even at distances of up to 900 km. The epicentral pattern of population development can be used to identify and prioritize adjacent landscape units for both reactive and proactive management strategies intended to minimize mountain pine beetle impacts.     

Development of polymorphic tetranucleotide microsatellites for pinyon jays (Gymnorhinus cyanocephalus)

The pinyon jay (Gymnorhinus cyanocephalus) is a primary seed disperser of pinyon pines (Pinus edulis and P. monophylla). Both the pinyon jay and the pinyon pines are experiencing significant decline. While the pinyon jay is a species of management value and conservation concern, little is known about its fecundity, among-flock dispersal, and population differentiation. We initiated genetic studies in pinyon jays using a hybridization enrichment technique to isolate seven polymorphic microsatellite repeats (AAAG and GATA) from the pinyon jay genome. A locus from the Mexican jay (Aphelocoma ultramarina) that amplifies robustly in pinyon jays is also reported. These eight loci revealed moderate to high diversity in an Arizona population of pinyon jays (4–36 alleles and H _O 0.42–0.90). As in other species, tetranucleotide repeats produced easily resolved amplification products.     

Variation on reaction norm in lodgepole pine natural populations

Variations on the norm of reaction among ten natural lodgepole pine populations sampled from three lodgepole pine subspecies (Pinus contorta ssp. contorta, ssp. latifolia and ssp. murrayana) were studied by using 20 year heights measured in 57 provenance test sites across interior British Columbia (B.C.). There were significant population by site interactions. Concurrent joint regression and the AMMI model were used to dissect these population by environmental interactions. Joint regression analysis indicated that three populations (from the northwest) had a negative linear regression coefficient with environmental deviation, three (from central and southeast sites) had a positive regression coefficient and four (from the southwest) had a zero regression coefficient. The AMMI model revealed a similar pattern of reaction norm among the ten populations. But the three significant IPCA axes, which captured twice as much of the G × E sum of squares than joint regression, were more effective in separating the ten populations and associating their performance with the climate of test sites and their origin. The variation patterns of reaction norm in lodgepole pine populations demonstrated that adaptation of lodgepole pine natural populations to the various physical environments, at sub-species as well as at population level, was due largely to a balance between selection for high growth potential in less severe environments and selection for high cold hardiness in severe environments. Received: 4 May 2000 / Accepted: 10 November 2000     

Seed-caching responses to substrate and rock cover by two <Emphasis Type="Italic">Peromyscus</Emphasis> species: implications for pinyon pine establishment

We examined whether pinyon mice (Peromyscus truei) and brush mice (P. boylii) could act as directed dispersal agents of pinyon pine (Pinus edulis) through differential responses to soil particle size and rock cover. In field experiments, we allowed mice to either cache pinyon seeds or recover artificially cached seeds (pilfer) from quadrats containing large- or small-particle soils. Both species placed most (70%) seed caches in small-particle soil. Pilfering was the same from both particle sizes in the first year, while more seeds were pilfered from large-particle soils in the second year. In separate experiments, rock cover interacted with soil particle size, with both species placing over 50% of their caches in small-particle soil with rock cover. Overall, we found greater seed-caching in small-particle soils near rocks, with equal or lower pilfering from small-particle soils, suggesting more seeds would survive in small-particle soils near rock cover. Three lines of evidence supported the hypothesis that mice could act as directed dispersers by moving pinyon seeds to beneficial microsites for germination and establishment. First, in greenhouse experiments, pinyon seed germination was 4 times greater in small-particle soil cores than in large-particle soil cores. Second, soils near rocks had significantly higher water content than areas of open soil at the driest time of the year, a critical factor for seedling survival in the arid southwestern USA. Third, 75% of juvenile pinyon trees were growing in small-particle soils, and 45% were growing near rock nurses.     

The role of mesotocin on social bonding in pinyon jays

The neuropeptide oxytocin influences mammalian social bonding by facilitating the building and maintenance of parental, sexual, and same-sex social relationships. However, we do not know whether the function of the avian homologue mesotocin is evolutionarily conserved across birds. While it does influence avian prosocial behavior, mesotocin's role in avian social bonding remains unclear. Here, we investigated whether mesotocin regulates the formation and maintenance of same-sex social bonding in pinyon jays (Gymnorhinus cyanocephalus), a member of the crow family. We formed squads of four individually housed birds. In the first, “pair-formation” phase of the experiment, we repeatedly placed pairs of birds from within the squad together in a cage for short periods of time. Prior to entering the cage, we intranasally administered one of three hormone solutions to both members of the pair: mesotocin, oxytocin antagonist, or saline. Pairs received repeated sessions with administration of the same hormone. In the second, “pair-maintenance” phase of the experiment, all four members of the squad were placed together in a large cage, and no hormones were administered. For both phases, we measured the physical proximity between pairs as our proxy for social bonding. We found that, compared with saline, administering mesotocin or oxytocin antagonist did not result in different proximities in either the pair-formation or pair-maintenance phase of the experiment. Therefore, at the dosages and time frames used here, exogenously introduced mesotocin did not influence same-sex social bond formation or maintenance. Like oxytocin in mammals, mesotocin regulates avian prosocial behavior; however, unlike oxytocin, we do not have evidence that mesotocin regulates social bonds in birds.