American Eel is undoubtedly one of the most studied freshwater fishes of North America. Many recent discoveries have added new insights that re-write important aspects of the “text book” knowledge of the species’ complex life history in ways that could have significant impacts on management. Despite all of this new information, debate about the species’ conservation status continues, and new threats, such as continued habitat loss and major clandestine fisheries driven by extremely high value in the global market, have further complicated management. Though USFWS recently decided that the species does not merit listing as “Endangered,” in 2012 Canada changed that country’s assessment of the species’ status from “Special Concern” (since 2006) to “Threatened” and IUCN upped its classification in 2013 to “Endangered.” Ontario has considered it “Endangered” since 2007. All U.S. Atlantic states vowed to work together to produce, in 1999, the American Eel Benchmark Stock Assessment, which mandated each state conduct standardized monitoring of recruitment and later, mandatory catch and effort monitoring. Given all that activity and data generation, it is remarkable that still so little is known about the populations of the Gulf of Mexico (GOM) and its tributary rivers that making any management decisions in that large, neglected part of the species’ range is virtually impossible. The Fishes of Texas Project team has been collating and improving the limited and scattered data on occurrences of the species in the region and concludes it important to promote a broad scale (Gulf of Mexico) collaborative community effort to acquire and share data and carefully curated specimens and, hopefully, develop a GOM-wide collaborative research and management plan like that implemented by Atlantic states. Here we’ll review the literature and state of knowledge about the species in Texas and GOM, and suggest ways to begin work toward such an effort.
Substantive progress was made on all major Project Activities in this first year:Activity 1. Coordinate and Facilitate Science and Conservation Actions for Conserving Texas Biodiversity - We expanded and strengthened UT-TPWD coordination, transitioning the relationship between these partners into a much more collaborative one than was previously realized. The flow of data between TPWD and the Fishes of Texas Project (supported in part by this project) has become much more bi-directional. Many newly collected TPWD specimens, agency databases, legacy data products and reports, and feedback from resource managers are now beginning to contribute substantively to growth and diversity (now including non-specimen-vouchered records) of data served through the FoTX Project’s websites. Work on cleaning and normalizing of FoTX’s online specimen-vouchered database continued, and the updated FoTX occurrence and distribution data are being actively used. Most recently they were used by this project, together with expert (TPWD, UT and others’) opinions, to develop recommendations on conservation status of native fishes of Texas’ Species of Greatest Conservation Need for TPWD’s consideration in anticipated updates to the Texas Conservation Action Plan. Within two months of this report, a new and substantially larger and improved version of the FoTX website/database and related collection of images, field notes, and ancillary datasets, will be formally announced.
Activity 2. Identify Priority Geographic Management Units for Conserving Fishes of Greatest Conservation Need - We used FoTX data in a systematic conservation area prioritization analysis to identify Native Fish Conservation Areas (NFCAs) for large portions of Texas where such comprehensive planning had not been previously carried out. Updated and new FoTX data for all Texas fish Species of Greatest Conservation Need (SGCN) were used in production of newly improved Species Distribution Models for input into this planning process, and the results of the planning exercise have already been integrated by TPWD into management prioritizations of both those species and the resultant NFCAs.
Activity 3. Develop Monitoring and Conservation Plans for Native Fish Conservation Areas - Monitoring and conservation plans were delivered to TPWD for all NFCAs identified in Activity 2.
Activity 4. Conduct Field-Based Surveys Detailed Biodiversity Assessments (i.e. Bioblitzing), and Citizen-Based Monitoring - Field surveys with detailed biodiversity assessments (“bioblitzes”) and citizen-based monitoring were conducted in three areas selected collaboratively by TPWD and FoTX Project staff from within the identified NFCAs: Nueces River headwaters, Big Cypress Bayou basin, and Village Creek basin. Along with this field effort, FoTX Project staff developed and circulated guidelines and best practices, and provided training for citizen-based monitoring that leverages iNaturalist for capture and reporting of photo-vouchered occurrence records in ways that will help assure scientifically useful data are obtained. All specimens acquired during these field efforts, and from many other routine specimen acquisitions from across the state (1845 total records/jars of specimens), were cataloged in the UT Fish Collection database. From there, these new records will soon be fed into GBIF, VertNet, FishNet2 and other major online data aggregators, including the online Fishes of Texas database.
Recent literature reviews of bioassessment methods raise questions about use of least-impacted reference sites to characterize natural conditions that no longer exist within contemporary landscapes. We explore an alternate approach for bioassessment that uses species site occupancy data from museum archives as input for species distribution models (SDMs) stacked to predict species assemblages of freshwater fishes in Texas. When data for estimating reference conditions are lacking, deviation between richness of contemporary versus modeled species assemblages could provide a means to infer relative biological integrity at appropriate spatial scales. We constructed SDMs for 100 freshwater fish species to compare predicted species assemblages to data on contemporary assemblages acquired by 4 independent surveys that sampled 269 sites. We then compared site-specific observed/predicted ratios of the number of species at sites to scores from a multimetric index of biotic integrity (IBI). Predicted numbers of species were moderately to strongly correlate with the numbers observed by the four surveys. We found significant, though weak, relationships between observed/predicted ratios and IBI scores. SDM-based assessments identified patterns of local assemblage change that were congruent with IBI inferences, however, modeling artifacts that likely contributed to over-prediction of species presence may restrict the stand-alone use of SDM-derived patterns for bioassessment and therefore warrant examination. Our results suggest that when extensive standardized survey data that includes reference sites are lacking, as is commonly the case, SDMs derived from generally much more readily available species site occupancy data could be used to provide a complementary tool for bioassessment.
Fishes of the family Salmonidae, including trout (Oncorhynchus), charr (Salvelinus), salmon (Oncorhynchus and Salmo), grayling (Thymallus) and whitefish (Prosopium), are expected to be particularly vulnerable to climate change because of their dependence on cold, clean water. Salmonids are among the most sought after fish by recreational anglers. In North America, their native range includes much of the continent from the Arctic Plains, along Pacific and Atlantic coasts, and throughout most mountainous regions (Behnke 2002). In Mexico, trout naturally occur in the mountainous regions of Baja California, and throughout the Sierra Madre Occidental as far south as the Rio Presidio and Rio Baluarte basins (Hendrickson et al. 2002). Brown trout (Salmo trutta) are native to Europe but have been broadly introduced in North America. Additionally, rainbow trout (O. mykiss) and brook trout (Salvelinus fontinalis) and other salmonids that are native to North America have been widely introduced into lakes, reservoirs, and river systems outside of their native ranges to increase angling opportunities.Climate change is likely to continue affecting salmonids throughout their ranges. Increasing air temperatures have been warming stream and lake temperatures (Schneider and Hook 2010; Asaak et al. 2012) with impacts ranging from growing stress and metabolic rates to loss of lower elevation habitats as waters warm (Eby et al. 2014; Keefer and Caudill 2015). Warmer conditions will also impact salmonids through changes in winter precipitation and altered flow regimes (Haak et al. 2010). Disturbance events, such as wildfires, floods, and drought, are likely to increase as well (Westerling et al. 2006) with resulting stream sedimentation (Goode et al. 2012). Many existing stressors for salmonids are likely to be made worse by climate change (Williams et al. 2015). For instance, non-native fishes, which now prey on and compete with native salmonids, are likely to increase in numbers and distributions as climate changes (Rahel and Olden 2008; Lawrence et al. 2014). The synergies that emerge from the combined effects of these stressors will be hard to predict with accuracy but are likely to magnify the negative consequences of climate change for coldwater fishes in North America.
The range of climate change impacts will not be equally harmful across all salmonid species. Although, all salmonids tend to be dependent on cold, clean water supplies, some species, such as bull trout (Salvelinus confluentus), Arctic grayling (Thymallus arcticus), and Dolly Varden (S. malma), are particularly sensitive to increasing temperatures and sedimentation (Selong et al. 2001; Jones et al. 2013). Changes in winter precipitation from snow to rain may impact fall-spawning species such as brook trout or brown trout to a greater degree than spring-spawning trout because of increased scouring of their egg beds (Wenger et al. 2011; Goode et al. 2013). Other species, such as California golden trout (O. aquabonita) and Lahontan cutthroat trout (O. clarkii henshawi), may occur in regions that are in the midst of sustained drought and particularly vulnerable to loss because of increasing isolation and small population size.
Despite our understanding of climate-driven impacts and known sensitivity of salmonids to warming conditions, predictions of future ecological conditions are complicated by the interactions among climate, biological, and geological processes. None of these factors act in isolation. The degree that warming and changes in disturbances impact particular habitats and species depends on the resilience of the habitat or species in question, including the interactions of biological, geomorphic and hydrologic systems. Impacts from climate change are likely to be more severe where stream and lake conditions are degraded or fragmented and less severe where habitats are robust and interconnected (Rieman and Isaak 2010). Unfortunately, many habitats of native salmonids have a legacy of pollution and fragmentation caused by dams, water diversions, agricultural runoff, and roads. The majority of native trout and charr species and subspecies occupy less than 25% of their historical habitat (Trout Unlimited 2015).
The purposes of this paper are to 1) review existing and likely future climate change impacts to salmonids in North America, 2) provide a primary bibliography for these impacts, and 3) describe how restoration can help trout adapt to climate change. The reader should keep in mind that the conservation status of most native salmonids already has declined as a result of the legacy of agricultural development, hydropower development, and the introduction of non-native species (Behnke 2002; Trout Unlimited 2015). Some taxa already are classified as vulnerable, threatened, or endangered by state, provincial, and federal agencies. Furthermore, as occupied habitat becomes increasingly fragmented and isolated, risks to climate-driven disturbances increase as well. Conservation efforts such as building artificial barriers to protect native trout from upstream invasions of non-native trout and warmwater fishes may result in further vulnerability to climate change because of range restrictions. Thus it is important to view increasing risk not just from the perspective of one or two factors but from the full variety of impacts that may accumulate over space and time.
Behavioral studies have often examined parental care by measuring phenotypic plasticity of behavior within a species. Phylogenetic studies have compared parental care among species, but only at broad categories (e.g., care vs. no care). Here we provide a detailed account that integrates phylogenetic analysis with quantitative behavioral data to better understand parental care behavior in the Cuatro Ciénegas cichlid, Herichthys minckleyi. We found that H. minckleyi occurs in a clade of sexually monochromatic or weakly dichromatic monogamous species, but that male and female H. minckleyi have dramatically different reproductive coloration patterns, likely as a result of sexual selection. Furthermore, we found that males are polygynous; large males guard large territories, and smaller males may attempt alternative mating tactics (sneaking). Finally, compared to the closely related monogamous Rio Grande cichlid, H. cyanoguttatus, males of H. minckleyi were present at their nests less often and performed lower rates of aggressive offspring defense, and females compensated for the absence of their mates by performing higher levels of offspring defense. Body color, mating system, and parental care in H. minckleyi appear to have evolved after it colonized Cuatro Ciénegas, and are likely a result of evolution in an isolated, stable environment.
Largemouth Bass Micropterus salmoides ranges naturally in Mexico fromthe binational Rio Grande basin, including Cuatro Ciénegas valley in the state of Coahuila, southward and eastward through two adjacent Gulf Coast drainages, the Río San Fernando and Río Soto la Marina in Nuevo León and Tamaulipas. Within this range, Florida Bass ⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚ has been introduced into reservoirs in at least the Río Grande and Soto La Marina basins. To assess the conservation status of native Mexican bass, we study genetic variability within and among Largemouth Bass populations and the degree of genetic introgression by Florida Bass within them. We sampled numerous localities in Cuatro Ciénegas, the San Fernando and Río Soto la Marina basins, and Vicente Guerrero Reservoir, where Florida Bass was introduced. We examined restriction-fragment polymorphisms within the 12S and 16S ribosomal RNA mitochondrial DNA genes and genotypes at two allozyme and ⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚- ment testing using the nuclear data. Largemouth Bass specimens possessed generally lower nuclear diversity, but higher mitochondrial diversity, than those of Florida Bass. Populations from Cuatro Ciénegas differed from those in the San Fernando and Soto la Marina basins. Nuclear analyses revealed three genetically pure populations in Cuatro Ciénegas (Charcos Prietos, Las Playitas, and Canal del Tío Julio), but hybrids in Río Garabatal and Mojarral Este. Another presumably pure Largemouth Bass population was found in Río El Tigre of the Soto La Marina drainage. Our results could be explained by geographic barriers, sexbiased dispersion, hybrid disadvantage, or selection for coadapted gene complexes. More extensive surveys are needed to fully assess the conservation status of native Largemouth Bass populations in México. We anticipate that these will reveal additional native diversity. Meanwhile, the remnant native populations delineated herein are important to protect and we advocate that their ranges be managed as genetic conservation areas.
Sharpnose shiner, Notropis oxyrhynchus, was recently listedas federally endangered Known from the Brazos and Colorado Rivers, but Colorado population believed to be introduced and now extinct Our species distribution models indicate sufficient habitat for the species to occur in the Colorado (Fig. 3). Our previous work (Fig. 1) to verify cyprinid museum specimens in the Colorado indicate 5 records of N. oxyrhynchus collected from 1884 to 1955 strongly suggesting nativity of the species (or a morphologically similar form) Visual examination of specimens from the Colorado suggest distinctive morphological (shape) differences compared to Brazos specimens We hypothesized Colorado population might be a separate or incipient species
Since Barbour proposed sympatric speciation to explain evolutionof silversides in the Lerma-Santiago basin, relatively little subsequent
study has been done. We assessed foraging patterns of four
sympatric silversides species (Chirostoma estor, Chirostoma grandocule,
Chirostoma attenuatum and Chirostoma patzcuaro) in Lago de
Pátzcuaro to understand resource partitioning and their sympatric
coexistence. We assessed the abundance of invertebrate prey in three
feeding habitats and measured physical and chemical habitat parameters
at two study sites. Fish were collected during the wet (September
1987) and dry (March 1988) seasons; a total of 242 gut contents were
analyzed. We evaluated the trophic guild of each species using the index
of relative importance (IRI), prey selectivity with the Ivlev Electivity
Index (E), dietary diversity using Shannon and Wiener diversity index
(H’), and diet overlap using Morisita index. All silverside species were
determined to be predaceous carnivores that feed mainly on nekton
and periphyton. Dietary diversity and prey selectivity patterns were
similar among species and diet overlap was >70%. Our data do not
support the proposition that coexistence of these four fish species is
maintained by dietary specialization. We hypothesize that sympatric
coexistence of atherinopsids in Lago de Pátzcuaro is explained by
food resource availability and ontogenetic variation in their diets. This
study highlights the importance of analyzing ecological patterns and
mechanisms as basic elements for designing conservation strategies of
species flocks, especially under habitat loss and introduction of exotic
species. Conservation efforts are urgent to preserve the rare evolutionary
process of sympatric speciation (habitat segregation) that is occurring
in other lakes in central Mexico, and probably already lost in the
Lago de Pátzcuaro, as a result of poor management and inadequate
Strategic conservation planning for broad, multi-species landscapes benefits from a data-driven approach that emphasizes persistence of all priority species populations and utilized landscapes, while simultaneously accounting for human uses. This study presents such an assessment for priority fishes of the Great Plains of the United States. Species distribution models for 28 priority fishes were created and incorporated into a prioritization framework using the open source software Zonation, accounting for species-specific connectivity needs and current fish habitat condition. Multiple additional assessments were then produced that i.) identify distinct species management units based on distance and compositional similarity of stream segments containing priority species, ii.) compare results of ranking species' conservation values at the local (state) and global scale, and iii.) provide 'bang-for-buck' perspectives, emphasizing richness of priority species, at state and major basin scales. Together, these analyses are intended to aid managers in effective allocation of conservation action with regards to imperiled fishes of the Great Plains. Implementation of a broad-scale multi-species approach such as this complements traditional reactive management and restoration by encouraging cooperation and coordination among stakeholders and partners, increasing efficiency of future monitoring and management efforts.
Numerous published reports indicate that records of occurrence of Sharpnose Shiner, Notropis oxyrhynchus, in the Colorado River basin of Texas are the result of an introduction, though the species is clearly native in the adjacent Brazos River basin. We discovered previously mis-identified specimens of N. oxyrhynchus that extend the record of presence of the species in the Colorado basin much further back in time than previous authors realized, and conclude that the species was almost certainly native there. However, lack of the species in any of the many collections made in the basin over the last half century indicates a low probability that it still persists there.
Abstract The variable platyfish (Xiphophorus variatus), native to Gulf Coast drainages of northern Mexico, is a popular aquarium fish with a long history of introduction globally. We document the first Texas occurrence of this species, and its persistence in highly urban Waller Creek in the city of Austin since at least 2004. The population appears to be limited to Waller Creek, having not yet been found in neighboring creeks where similar habitat exists. We observed individuals in situ and in the lab surviving in 7°C water, well below published thermal minima, and report its persistence through one of the coldest winters in Austin's recorded history. Its persistence may be due to a combination of its cold tolerance and the presence of thermal refuges. In the lab we found that individuals purchased in a local pet store and individuals from Waller Creek had the same cold tolerance. , Resumen El pez espada de Valles (Xiphophorus variatus), nativo de las cuencas afluentes del golfo de México del norte de México, es una especie popular de acuario con una historia larga de introducciones globales. Aquí documentamos la primera ocurrencia de la especie en Texas y su persistencia en un arroyo urbano, Waller Creek en la ciudad de Austin, a partir de por lo menos 2004. La población parece limitada a Waller Creek porque aún no se ha encontrado en arroyos cercanos con hábitat similar. Observamos individuos in situ y en el laboratorio sobreviviendo en agua de 7°C, mucho más frio que la mínima tolerancia termal publicada, y reportamos su persistencia a través de uno de los inviernos más fríos en la historia de Austin. Su persistencia puede ser atribuida a una combinación de su tolerancia al frío y existencia de refugios termales. En el laboratorio, individuos comprados en una tienda local de acuario e individuos de Waller Creek mostraron la misma tolerancia al frío.
The desert, its resources and researchers! The two intersected for the 6th time as the Chihuahuan Desert Research Institute hosted over 200 participants for the symposium held at Sul Ross State University, 14th-17th of October 2004. The cumulative years of research experience, knowledge, and publications among participants was truly impressive, and all tied together at the conference by their individual care for, and research interest in, the natural resources of the Chihuahuan Desert region. By its bi-national nature, the conference represents a broad focus on the rich and complex biodiversity, ecosystems, and biogeography of the Chihuahuan Desert, with even greater representation at the conference (topics, titles, and authors) of the northern portion of the desert in northern México and the southwestern United States of America. As at the previous five conferences, the topics were diverse.The human dimension in the desert (uses, impacts, influences, and appreciation) was included and this time, a major synthetic overview of ecoregional planning and assessment of conservation concerns, values (species, natural communities, and ecosystems), specific sites, and predominant threats throughout the entire Chihuahuan Desert (click here for a complete copy of the Ecoregional Conservation Assessment for the Chihuahuan Desert).The potency of such a convention is of course, much more than just the excellent and professional presentation of papers and posters. It is also the hallway and after-hours conversations, exchanges of ideas and recollections, reunions and introductions. This conference covered a depth and breadth that has become the hallmark of the conference by reputation and inclusiveness. The range of topical sessions spanned from species-specific papers and sessions; to focus on specific conservation sites; to groupings like the desert herpetofauna and mammals; to sessions about aquatics, cacti, and exotic species; to ecosystems; and then the composite Chihuahuan Desert conservation overview.
The conference was launched by Chihuahuan Desert Research Institute Executive Director Cathryn Hoyt’s conference welcome, which was followed by the plenary Keynote Address given by Dr. Dean Hendrickson of the University of Texas at Austin. He set the tone for the conference with a sterling conservation message and alarm for one of the desert’s most notable biodiversity treasures—Cuatro Cienégas, Coahuila. His presentation looked at the history and future of Cuatro Cienégas and the effects of regional problems that are catching up in this time-lagged gem of the Chihuahuan Desert.
The threads and themes of the individual presentations and topical sessions also spanned the geography and topography of the northern Chihuahuan Desert. The basin-and-range physiography was covered from the grasslands of the basins to the forested sky island mountain ranges. Water is the most crucial and vital (and certainly limited and limiting) resource of the desert, hence the topical foci on aquatic resources from rare fishes and turtles to invertebrates and limnology in several sessions. There were topical sessions such as a panel presentation and group discussion on exotic species including salt cedar (Tamarix) and riparian restoration along the Rio Grande/ Rio Bravo, and a separate session just on exotic animals that threaten species, habitats, and natural communities, and which warrant concern and management.
This conference took on a markedly different angle from previous conferences in that there was considerable focus on landscape ecology, systems, and processes. An elaborate and sequentially-presented multi-session topic led by the Jornada Experimental Station research team covered landscape linkages and cross-scale interactions in the northern Chihuahuan Desert rangeland context; tying together soils, hydrology, and ecological management of complex ecological drivers within highly dynamic systems. Five full sessions were structured with a particular emphasis on semiarid grasslands specifically, with three on grassland vegetation ecology and restoration, another covering ecology of semiarid grassland mammals, and yet another devoted to semiarid grassland birds. One session included fire effects and ecological ramifications, trajectories, and outcomes of fire in the desert and mountains.
Finally, a full session was dedicated to natural resource interpretation and informal education within and about the desert. Topics included interpretation from a national park perspective; interpretation as a conservation tool; the importance of place and familiarity with an ecoregion; bioregional education; field schools, and backyard habitats. The unifying theme was tying the natural resources of the desert to the people who use, visit, reside within, conduct research, recreate, or merely appreciate the desert and wanting to know it better, and fuller. To this end, there was a special multi-day workshop on interpretive guide training and certification offered in conjunction with the Symposium. Held prior to the actual symposium, and hosted by the Chihuahuan Desert Research Institute in association with the National Association for Interpretation (the umbrella organization of natural and cultural resource interpretation), the program was facilitated and led by a professional interpretive trainer as a hands-on field school at nearby Camp Mitre Peak. Scholarships for attendees were generously provided by the Rio Grande Institute.
An additional rangeland health workshop was conducted following the Symposium. The workshop was titled “Interpreting Indicators of Rangeland Health: an Introduction to the Qualitative Rangeland Assessment Protocol” led by scientists from the USDA/ARS Jornada Experimental Range.
Sul Ross State University’s Museum of the Big Bend featured an exhibit developed in conjunction with the conference that opened as the conference began titled “Boundaries to Blair: Eight Scientists in the Big Bend.” The display included books and archival materials that highlighted the biological investigations and scientists of the borderlands from the early days of settlement up to the baseline-establishing biotic province surveys of W. Frank Blair, a University of Texas zoologist who was a keen early supporter of CDRI in its formative years.
The conference truly had at least bi-national representation with a registration of approximately 200 people. Just as significantly, the total number of presenters of technical presentations included 90 papers (by a cumulative 256 authors or coauthors) and 16 posters by 46 authors or coauthors. There were 26 moderated sessions, with student award competitions for the best paper presented from among 17 student competitors and for the best student poster.
AbstractNeuroendocrine pathways that regulate social behavior are remarkably conserved across divergent taxa. The neuropeptides arginine vasotocin/vasopressin (AVT/AVP) and their receptor V1a mediate aggression, space use, and mating behavior in male vertebrates. The hormone prolactin (PRL) also regulates social behavior across species, most notably paternal behavior. Both hormone systems may be involved in the evolution of monogamous mating systems. We compared AVT, AVT receptor V1a2, PRL, and PRL receptor PRLR1 gene expression in the brains as well as circulating androgen concentrations of free-living reproductively active males of two closely related North American cichlid species, the monogamous Herichthys cyanoguttatus and the polygynous H. minckleyi. We found that H. cyanoguttatus males bond with a single female and together they cooperatively defend a small territory in which they reproduce. In H. minckleyi, a small number of large males defend large territories in which they mate with several females. Levels of V1a2 mRNA were higher in the hypothalamus of H. minckleyi, and PRLR1 expression was higher in the hypothalamus and telencephalon of H. minckleyi. 11-ketotestosterone levels were higher in H. minckleyi, while testosterone levels were higher in H. cyanoguttatus. Our results indicate that a highly active AVT/V1a2 circuit(s) in the brain is associated with space use and social dominance and that pair bonding is mediated either by a different, less active AVT/V1a2 circuit or by another neuroendocrine system.