Browsing by Subject "Cryptic species"

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The coexistence of ecologically similar species
(2013-12) Smith, Geneviève Kathleen; Leibold, Mathew A.
The biological diversity on planet Earth is astounding. Understanding the origins of this diversity, and how it is maintained, are the twin goals of ecology and evolutionary biology. An early and oft-repeated insight in this investigation is that that similar organisms cannot coexist indefinitely. Theory predicts that individuals and species will compete for limited resources and whichever has even a slight advantage will drive all others extinct in a process known as ‘competitive exclusion’. By diversifying, species avoid competition, thereby ‘stabilizing’ their coexistence. Yet natural systems often display levels of diversity that are surprisingly high, given this theory and investigations of how the similarity of coexisting species is maintained have received much less attention. Using a combination of field studies and experiments I demonstrate that highly similar species of freshwater amphipods may compete for resources without resulting in competitive exclusion. These findings suggest that there exist a range of interactions among Hyalella amphipods, ranging from strong stabilizing effects due to ecological trade-offs, to weakly stabilizing effects, to a total lack of stabilizing effects among various pairs of species in this system. These findings demonstrate how the relative strength of stabilizing forces may vary among coexisting species. Although much effort has been dedicated to enumerating and classifying the ways in which ecological and evolutionary forces promote diversity among species, there has been far less attention paid to mechanisms such as convergent evolution, habitat filtering, competition for non-substitutable resources, and non-ecological speciation, among others. I surveyed current theory that may explain the high levels of similarity among species often found in natural systems. I describe how several ecological and evolutionary mechanisms may operate to promote the coexistence of similar species and present results from new theoretical combinations of mechanisms to demonstrate how they may further act in concert with one another.
Long-term dynamics and theoretical considerations in coral holobiont adaptation
(2024-05) Scott, Carly Brielle ; Matz, Mikhail V.; Ostling, Annette; Narasimhan, Vagheesh M; Lauren Toth
Corals are predicted to adapt to environmental change in two ways: through the nuclear evolution of the host and/or through acquiring new, more suitable symbiotic partners. Given the rapid rate of climate change, considerable attention has focused on the latter, as new symbiotic partnerships could, in theory, be formed within one coral generation. Underlying this idea are the assumptions that coral-holobiont partnerships are flexible in response to the environment, and that their flexibility benefits the host. However, the contributions of host genetics, local environment, and time in structuring the holobiont have not been estimated in tandem. This work directly addresses these factors across extended temporal scales through: (1) establishing the feasibility of ancient (6,000-year-old) DNA in coral reef research, (2) determining what structures the holobiont in centuries-old massive corals, and (3) providing a novel theoretical framework for why holobiont shifts occur. From this research, it is clear that host genetics play a strong role in structuring the coral holobiont, suggesting host evolution is essential for reef persistence in future conditions. However, despite many holobiont members remaining present over thousands of years, the local environment and age class have a significant role in structuring the bacterial portion of the coral holobiont. Finally, theoretical modeling of coral bleaching suggests that observed shifts in coral-holobiont partnerships may arise not from adaptation to increasing thermal stress, but rather underlying changes in host demography. Together, these results demonstrate that the evolutionary potential of the coral host cannot be overlooked, as holobiont reassembly alone will likely not create more robust reefs.
(Vol. 04, 2001-12) A New Cryptic Species of Nemophila (Hydrophyllaceae) from Texas and the Leptotypification of N. Phacelioides Nuttall
(2001-12) Simpson, Beryl B.; Helfgott, D. Megan; Neff, John L.
Nemophila sayersensis, a cryptic species restricted to sandy, nutrient poor soils and sister to N. phacelioides, is described and illustrated. While examining type material of N. phacelioides and that of its synonyms, it became obvious that the species had never been typified despite its widespread distribution and treatment in numerous revisions. We here typify all named entities associated with the two species.