Jacob F. Schaefer

Shared and unique morphological responses of stream fishes to anthropogenic habitat alteration

Understanding population-level responses to novel selective pressures can elucidate evolutionary consequences of human-altered habitats. Stream impoundments (reservoirs) alter riverine ecosystems worldwide, exposing stream fishes to uncommon selective pressures. Assessing phenotypic trait divergence in reservoir habitats will be a first step in identifying the potential evolutionary and ecological consequences of stream impoundments. We tested for body shape divergence in four stream-adapted fishes found in both habitats within three separate basins. Shape variation among fishes was partitioned into shared (exhibited by all species) and unique (species-specific) responses to reservoir habitats. All fishes demonstrated consistent significant shared and unique morphological responses to reservoir habitats. Shared responses were linked to fin positioning, decreased body depths and larger caudal areas; traits likely related to locomotion. Unique responses were linked to head shape, suggesting species-specific responses to abiotic conditions or changes to their trophic ecology in reservoirs. Our results highlight how human-altered habitats can simultaneously drive similar and unique trait divergence in native populations.

Modular Experimental Riffle–Pool Stream System

Abstract We describe a modular method for building a large, outdoor experimental stream system that has great flexibility for research projects in fish ecology, behavior, conservation, or management. The system has been in use for more than a decade at the University of Oklahoma Biological Station (Kingston, Oklahoma) and has been used with modification at four other research facilities in the Midwest. Here, we document the system in detail, including specifications for construction of the original system and modifications or improvements at other sites. The system uses commercially available, customized fiberglass round tank and trough units that can be configured in many different ways to create flowing pool and riffle habitats. The system appears to be a good mimic of small natural streams based on system flow rates, establishment of natural substrates and cover, stream chemistry relative to that of a natural creek, and fish behaviors. At least 39 fish species have been used successfully in 1–14-month ...

Morphological divergence and flow-induced phenotypic plasticity in a native fish from anthropogenically altered stream habitats

Understanding population-level responses to human-induced changes to habitats can elucidate the evolutionary consequences of rapid habitat alteration. Reservoirs constructed on streams expose stream fishes to novel selective pressures in these habitats. Assessing the drivers of trait divergence facilitated by these habitats will help identify evolutionary and ecological consequences of reservoir habitats. We tested for morphological divergence in a stream fish that occupies both stream and reservoir habitats. To assess contributions of genetic-level differences and phenotypic plasticity induced by flow variation, we spawned and reared individuals from both habitats types in flow and no flow conditions. Body shape significantly and consistently diverged in reservoir habitats compared with streams; individuals from reservoirs were shallower bodied with smaller heads compared with individuals from streams. Significant population-level differences in morphology persisted in offspring but morphological variation compared with field-collected individuals was limited to the head region. Populations demonstrated dissimilar flow-induced phenotypic plasticity when reared under flow, but phenotypic plasticity in response to flow variation was an unlikely explanation for observed phenotypic divergence in the field. Our results, together with previous investigations, suggest the environmental conditions currently thought to drive morphological change in reservoirs (i.e., predation and flow regimes) may not be the sole drivers of phenotypic change.

Hybridization and reproductive isolation among syntopic populations of the topminnows Fundulus notatus and F. olivaceus

Fundulus notatus and Fundulus olivaceus are two closely related topminnow species that exhibit similar ecological niches and broad, largely overlapping, North American ranges extending throughout much of the Mississippi River drainage as well as the coastal drainages of the Gulf of Mexico. Previous studies have suggested that these two species are reproductively compatible despite cytogenetic differences and will hybridize when syntopic. We used nuclear and mtDNA loci to assess levels of hybridization and test for introgression in syntopic populations of these two species in four drainages in southern Illinois. Although hybridization was detected in all syntopic populations, an assessment of the proportion of hybrid individuals indicated a deficiency of hybrids relative to expectations under random mating. We determined that, although mtDNA introgression was prevalent and extended beyond the zones of contact, evidence of nuclear introgression was limited to the zone of sympatry.

Derivation of the freshwater fish fauna of Central America revisited: Myers's hypothesis in the twenty-first century

Although attempts to understand Central American freshwater fish provincialism date to the 1960s, early efforts lacked the wealth of distributional data now available. Biogeographic work on Central American freshwater fishes has been largely descriptive and regional, and lacked a broader synthesis. Here we use parsimony analysis of endemicity (PAE) to elucidate faunistic relationships between major drainages and to delineate areas of endemism. We then perform a Brooks parsimony analysis (BPA) on the resulting areas. The PAE recovered a primary division between four Pacific and six Atlantic slope areas of endemism. In contrast, the BPA recovered two Central American geographic clades, one sharing a history with North America and the other with South America. Fish diversity is uneven across Central America, with greater diversity in areas adjacent to the more species‐rich regions of North and South America. In northern and nuclear Central America, the paucity of ostariophysan freshwater fishes such as catfishes and characins (groups that dominate adjacent regions) contrasts with high species richness of poeciliids and cichlids. Results of this study are consistent with Myers hypothesis that poeciliids and cichlids dispersed to Northern or Nuclear Middle America early in the Cenozoic, long before the Plio‐Pleistocene rise of the Isthmus of Panama.

Ecological and genetic assessment of spatial structure among replicate contact zones between two topminnow species

The spatial structure of contact zones is often described as disjunct, diffuse or mosaic and presumed to be related to underlying ecological gradients. However, the ecology of contact zones, how they are structured, and if that structure is predictable based on the strength and nature of ecological gradients is unknown. Large spatial scales and the unreplicated nature of many of the best studied contact zones has made it difficult to codify broader ecological patterns. Freshwater stream fish contact zones have the advantage of being potentially replicated with well defined boundaries and predictable linear gradients (river continuum concept). We sampled four replicate topminnow (Fundulus olivaceus and F. notatus) contact zones in Gulf of Mexico drainages. In each, we quantified contact zone spatial structure and the strength of ecological gradients (habitat, physicochemical variables and fish community functional traits). All three types of contact zone structure were represented. Systems with weaker gradients had diffuse contact zones, low species richness and were numerically dominated by generalist species. Rates of hybridization were also variable among systems. There was no hybridization detected in the mosaic zone while hybrids were found at most of the co-occurrence sites in the diffuse and disjunct zones. Overall, local ecology clearly influences contact zone structure and the two species interact in fundamentally different ways in these four systems.

Tests of Reproductive Isolation Among Species in the Fundulus notatus (Cyprinodontiformes : Fundulidae) Species Complex

We assessed prezygotic (probability of spawning) and postzygotic (hatching success) reproductive isolation among the three ecologically and morphologically similar species in the Fundulus notatus species complex. We employed a multi-generation breeding experiment to test the hypotheses that karyotypic differences, body size differences, or geographic isolation among populations will increase pre or postzygotic reproductive barriers. Overall, prezygotic barriers were strong and postzygotic barriers weak in crosses of non-hybrid heterospecifics (F1 hybrid crosses) while prezygotic barriers were weaker and postzygotic barriers stronger in crosses involving hybrid individuals (F2 hybrid crosses and backcrosses). Prezygotic barriers among the two smaller species (Fundulus notatus and F. euryzonus) broke down rapidly; first generation hybrids spawned (F2 hybrid crosses and backcrosses) as frequently as parental forms in intraspecific crosses. There was no increase in postzygotic barriers among species with cytogenetic differences. There were increased prezygotic, but not postzygotic, barriers among geographically isolated populations of one species. While pure males and females were just as likely to spawn with hybrids, some types of hybrid females suffered from increased sterility, but not inviability, over hybrid males. Female sterility was only seen in hybrids with a Fundulus euryzonus parent, while other female hybrids produced viable eggs.

A Delineation of Nuclear Middle America Biogeographical Provinces Based on River Basin Faunistic Similarities

The biogeographical patterns of the obligate freshwater fishes of Nuclear Middle America, a region that expands from southern Guatemala to northern Nicaragua, are described herein. Historically, three broad ichthyological provinces have been assigned to Nuclear Middle America: the Usumacinta, and the San Juan in the Atlantic slope and the Chiapas-Nicaragüense in the Pacific slope. With the use of correspondence analysis and unweighted pair group method with arithmetic mean cluster analysis of a presence/absence matrix of 76 obligate freshwater fishes, we identified four ichthyological provinces in Nuclear Middle America: (1) the Honduras and Guatemala Caribbean Highlands Province, (2) the Honduras and Nicaragua Mosquitia Province, (3) the Chiapas-El Salvador-Nacaome Province, and (4) the Choluteca and Nicaragua Pacific Province. Differences between provinces in species composition and species turnover between provinces were tested by analysis of similarity, the calculation of beta-diversity indices and an indicator species analysis. We then further characterized each province by identifying the number of endemics and classifying species according to their salinity tolerance. The most striking patterns of Nuclear Middle America freshwater fish distribution are its paucity of primary freshwater fishes and limited numbers of endemics. The four ichthyological provinces are distinct as indicated by the ANOSIM and beta-diversity analysis, although one province showed low beta-diversity values. These results suggest that, despite of the active geological history that characterized the region, there has been limited isolation of species in any given province, and historical drainage connectivity has been high.

Dynamics of Near-Coastal Fish Assemblages following the Deepwater Horizon Oil Spill in the Northern Gulf of Mexico

AbstractCoastal ecosystems along the northern Gulf of Mexico are highly productive and are affected by fishing and petroleum industries in different, sometimes contrasting, ways. As a result of the Deepwater Horizon (DWH) oil spill in April 2010, oil and oil dispersants were introduced into the northern Gulf of Mexico. At the same time, large portions of the Gulf of Mexico were closed to commercial and recreational fishing for most of the 2010 summer. This presented a unique opportunity to study the dynamics of a fish assemblage exposed to changes in two disparate types of anthropogenic disturbances. We compared assemblage data for near-coastal fish (456 samples representing over 45,000 individuals and 109 species) from pre-DWH (before 2010) and post-DWH (2011–2014) to assess potential changes in abundance, diversity (alpha, beta, and gamma), and assemblage structure. In contrast to predicted oil-induced mortality, post-DWH assemblages were characterized by high abundance in 2011 (CPUE across all species ...

A new species of Profundulus (Cyprinodontiformes: Profundulidae) from the Honduran central highlands

A new species of Profundulus, Profundulus portillorum, from the Honduran central highlands is described. Profundulus portillorum belongs to the Profundulus labialis species group and is distinct from the Profundulus punctatus species group in that it lacks a humeral spot and less than half of the caudal fin is scaled. Within the P. labialis species group, P. portillorum has a more slender body, smaller eye, fewer anal rays, caudal rays and lateral-line scales than other species. Forty-one specimens were collected around emergent vegetation in the margins of two small (2-5 m in width, 20-40 cm in depth), high-elevation (1300 m) tributaries of the Río Calam within the Río Ulúa drainage. These specimens represent the easternmost collection of any Profundulus and the first collection of any member of the P. labialis species group from Honduras.