Showing papers by "Jane C. Marks published in 2005"

Plant genes link forests and streams

Abstract: Although it is understood that the composition of riparian trees can affect stream function through leaf litter fall, the potential effects of genetic variation within species are less understood. Using a naturally hybridizing cottonwood system, we examined the hypothesis that genetic differences among two parental species (Populus fremontii and P. angustifolia) and two groups of their hybrids (F1 and backcrosses to P. angustifolia) would affect litter decomposition rates and the composition of the aquatic invertebrate community that colonizes leaves. Three major findings emerged: (1) parental and hybrid types differ in litter quality, (2) decomposition differs between two groups, a fast group (P. fremontii and F1 hybrid), and a slow group (P. angustifolia and backcross hybrids), and (3) aquatic invertebrate communities colonizing P. fremontii litter differed significantly in composition from all other cross types, even though P. fremontii and the F1 hybrid decomposed at similar rates. These findings are in agreement with terrestrial arthropod studies in the same cottonwood system. However, the effects are less pronounced aquatically than those observed in the adjacent terrestrial community, which supports a genetic diffusion hypothesis. Importantly, these findings argue that genetic interactions link terrestrial and aquatic communities and may have significant evolutionary and conservation implications.

Aquatic invertebrates of cuatro ciénegas, coahuila, méxico: natives and exotics

Abstract: A recent survey of benthic macroinvertebrates of the Cuatro Cienegas basin found 118 species in the 21 sites collected. Four exotic macroinvertebrates that could threaten the native biota were found within or near the basin.

Habitat segregation among trophic morphs of the Cuatro Ciénegas cichlid (Herichthys minckleyi)

Abstract: Herichthys minckleyi is an endangered, trophically polymorphic cichlid endemic to the Cuatro Cienegas basin of Coahuila, Mexico. A molariform morph has stout pharyngeal teeth whereas a papilliform morph has numerous fine pharyngeal teeth. Individuals with intermediate pharyngeal dentition also exist, as does yet another morph, called piscivore. Previous studies indicated that morphs utilize different food sources, thus suggesting morph-specific spatial segregation, since food resource availability is spatially heterogeneous. We present data from an observational study of all morphs (but focusing on the three most common, normal-bodied ones – molariform, papilliform and intermediate) in a single spring pool, Poza Mojarral Oeste. We analyzed morph distribution in relation to habitat types, and document morph-specific differences in feeding behavior. Spatio-temporal habitat partitioning was also investigated. Habitat use by molariform, papilliform, and intermediate morphs was found to be non-random. Morphs differed in habitat use, albeit with considerable overlap. Strong segregation among morphs was not detected in any season or time of day, but habitat use patterns varied seasonally within each morph and were consistently different among morphs. All morphs behave basically as feeding generalists. This endangered species may prove more difficult to manage than other, non-polymorphic species. It is clearly important to manage not only for the maintenance of the species, but also for maintenance of its different morphs, which our study indicates may each require different mixes of habitat types. We thus hypothesize that any changes in habitat heterogeneity will lead to altered proportions of the different morphs of the species.

'All effects of a gene on the world': Extended phenotypes, feedbacks, and multi-level selection

Abstract: In a potentially influential article, Whitham et al. (2003) adopted the concept of the extended phenotype (Dawkins, 1982) to suggest a novel perspective on community genetics and evolution. Their purpose was to examine “how the extended phenotypes of genes have important consequences at community and ecosystem levels”, keeping in mind “the ultimate consequence of heritable extended phenotypes” (p. 560): community evolution by natural selection. We take issue with two aspects of the interpretation of extended phenotypes (EPs) given by Whitham et al. (2003) and adopted elsewhere in the emerging literature of community and ecosystem genetics (references below). First, we clarify that the functional concept of the EP (sensu Dawkins, 1982) is, in an important sense, more precise than employed by recent authors. Second, natural selection of so-called ‘extended phenotypes’ involves an unlikely mechanism of selection and instead implies the existence of adaptive ‘community phenotypes’. As part of a special feature on community genetics (Ecology, volume 84, March 2003), Whitham et al.’s (2003) perspective was followed by a number of critical reviews. Critics ranged from optimistic (Cavender-Bares & Wilczek, 2003; Wade, 2003; Wilson & Swenson, 2003; and see Mitton, 2003) to highly skeptical of the concept of community evolution by natural selection (Collins, 2003; Morin, 2003; Ricklefs, 2003). Unfortunately, however, none of these critics revisited Dawkins’ (1982) original concept of the extended phenotype to adequately question its relevance to community genetics. Consequently, no critic fully explored the causal link between community-level genetic effects and the survival of the genes involved. The extended phenotype is an aid for understanding genetic effects as adaptations. Specifically, Dawkins (1982, p. 207) considered phenotypes to be “devices by which genes lever themselves into the next generation, or barriers to their doing so”, and demonstrated that adaptive phenotypes need not be restricted to the boundaries of discrete ‘vehicles’ (e.g., organisms or groups). (Hence, beaver dams and bird nests are phenotypes designed by natural selection even though they exist outside of the bodies of beavers and birds, respectively, that construct them). Of course, not all genetic effects on the world at large are adaptive; many will be the side effects of other adaptations, and have no influence on the survival of the genes involved. For those incidental consequences, Dawkins (1982, p. 207) concluded, “we do not bother to regard them as phenotypic expressions of genes, either at the conventional or the extended phenotypic level”. Whitham et al. (2003, p. 560) do precisely this; they used a broad-sense concept of the extended phenotype as “the effects of genes at levels higher than the population”—which presumably include incidental side effects that act as neither tools nor barriers to gene survival. Many of the proposed ‘extended phenotypes’ from Whitham et al. (2003) stand out as incidental side effects. They suggested, for example, that genes for the timing of salmon migration and spawning have the extended phenotypic effect of enhanced riparian plant growth. In the logic of the EP, their example suggests that enhanced riparian plant growth is the phenotypic effect of a gene ‘for’ plant growth, sitting in the bodies of salmon but acting via behavioural modification of the animals that transfer salmon-derived nutrients to the forest. We see the effects of this gene today because it has outlasted rival alleles that do not have the effect of enhancing riparian plant growth. Of course, it is difficult to conceive of any immediate effects that could possibly benefit the next generation of salmon that carry the enhanced plant growth allele. Hence, it seems implausible that enhanced plant growth actually represents a device by which salmon genes ‘lever themselves into the next generation’. Similarly, recent investigations in community genetics that allude to ‘extended phenotypes’ (see Bailey et al., 2004; Fischer et al., 2004; Schweitzer et al., 2004) describe higher-order genetic effects that can be understood as incidental consequences. In most cases, the authors demonstrate 1) that genetic variation exists for some trait in a given species, and 2) that variation in that trait correlates with a communityor ecosystem-level effect. In no case, however, is the intention to determine whether the higher-order effect serves to increase the frequency of alleles ‘for’ that effect, at the expense of alternative alleles. Without addressing this final criterion, there is no justification for invoking the concept of the extended phenotype. Given that most community-level effects seem implausible as true extended phenotypes, how might they be considered adaptive? Whitham et al. (2003) adopted a multi-level selection approach as their model for the evolution of ‘extended phenotypes’, in which higher-order FORUM The overextended phenotype

Do movement patterns differ between laboratory and field suction feeding behaviors in a Mexican cichlid

Abstract: We analyzed feeding behavior of individuals of Herichthys minckleyi, the Cuatro Cienegas cichlid, under laboratory conditions and freely behaving in their natural environment using high-speed video imaging. In a multivariate analysis of suction feeding behaviors there was no clear grouping of feeding events based on the environment, which suggests that most of the variability in the data was unrelated to differences between lab and field behaviors. In fact, the variability within an environment was far greater than the variability between the two environments. These results suggest that laboratory studies can accurately describe the kinematics of behaviors seen in the field. However, although lab based studies can quantify behaviors seen in the field, natural habitats are complex and provide individuals with the opportunity to exploit a wide range of food types and microhabitats, which may elicit behaviors not observed in the laboratory. However, feeding behaviors observed in the lab are representative of frequently used feeding behaviors in the field, at least for this species. Thus, we suggest that laboratory studies of feeding behavior, particularly those that test biomechanical or performance-based hypotheses can be extrapolated to natural environments.

Habitat Segregation among Trophic Morphs of the Cuatro Ciénegas Cichlid (Herichthys minckleyi) Segregación de hábitat entre formas tróficas de la mojarra de Cuatro Ciénegas ( Herichthys minckleyi)

Abstract: Herichthys minckleyi is an endangered, trophically polymorphic cichlid endemic to the Cuatro Cienegas basin of Coahuila, Mexico. A molariform morph has stout pharyngeal teeth whereas a papilliform morph has numerous fine pharyngeal teeth. Individuals with intermediate pharyngeal dentition also exist, as does yet another morph, called piscivore. Previous studies indicated that morphs utilize different food sources, thus suggesting morph-specific spatial segregation, since food resource availability is spatially heterogeneous. We present data from an observational study of all morphs (but focusing on the three most common, normal-bodied ones ‐ molariform, papilliform and intermediate) in a single spring pool, Poza Mojarral Oeste. We analyzed morph distribution in relation to habitat types, and document morph-specific differences in feeding behavior. Spatio-temporal habitat partitioning was also investigated. Habitat use by molariform, papilliform, and intermediate morphs was found to be non-random. Morphs differed in habitat use, albeit with considerable overlap. Strong segregation among morphs was not detected in any season or time of day, but habitat use patterns varied seasonally within each morph and were consistently different among morphs. All morphs behave basically as feeding generalists. This endangered species may prove more difficult to manage than other, non-polymorphic species. It is clearly important to manage not only for the maintenance of the species, but also for maintenance of its different morphs, which our study indicates may each require different mixes of habitat types. We thus hypothesize that any changes in habitat heterogeneity will lead to altered proportions of the different morphs of the species.