Dr. Luke Shoo and a group of amphibian conservation biologists recently published a paper titled "Engineering a future for amphibians under climate change" in the Forum section of the Journal of Applied Ecology. The paper does not present new research, but instead proposes habitat management recommendations for conserving amphibians under conditions of rapidly changing climate. Given that they apply to "amphibians" in the broadest sense, the recommendations are very general. They also entail a rather active level of habitat management, as alluded to by "engineering" in the title.
Among the recommendations is a category of "enhancement and restoration of breeding sites," which, of course, is major component of the rationale for the USC/ESF Vernal Pool Restoration Project. They give a brief summary and assessment of previous efforts to construct or restore amphibian breeding sites, and a few general considerations to improve success. In particular, I was pleased to discover a paper in the journal Hydrobiologia titled "Restoring ponds for amphibians: a success story." The European authors report on an ambitious pool construction and restoration effort in Estonia on behalf of imperiled spadefoot toads and crested newts. Their approach, results, and recommendations are especially relevant to us because of their emphases on building clusters of diverse ponds, and in their explicit consideration of terrestrial habitat conditions.
I agree that such active habitat management recommendations can be helpful in mitigating effects of climate change, but I also suggest that some of them are appropriate for mitigating the more traditional threats to amphibian populations such as habitat loss, emerging infectious diseases, and invasive species. It is surprising that, for the time being, there is such a small number of case studies and success stories in the published literature...
Jim Arrigoni, SUNY ESF
Showing posts with label literature. Show all posts
Showing posts with label literature. Show all posts
Tuesday, February 22, 2011
Wednesday, December 15, 2010
Unexpected ecological function of smaller, ephemeral pools
A recent paper published in the journal Ecology adds to the evidence that bigger is not always preferable when it comes to wetlands, and also illustrates the importance of understanding the intricate details of natural history in complex ecological systems:
Altermatt F, Ebert D. 2010. Populations in small, ephemeral habitat patches may drive dynamics in a Daphnia magna metapopulation. Ecology 91: 2975-2982.
Daphnia are miniscule crustaceans that typically comprise a substantial fraction of the zooplankton in lentic freshwater systems throughout the world. They are a vital component of larval spotted salamander diet, particularly early in their development (see Joseph Freda's 1983 paper in Journal of Herpetology [vol. 17, pp. 177-179], "Diet of larval Ambystoma maculatum in New Jersey"). Daphnia are notable in that they employ multiple modes of reproduction, depending on their circumstances. When environmental conditions are favorable, females reproduce parthenogenetically -- they essentially clone themselves, which results in the production eggs that hatch into females. However, when environmental conditions take a turn for the worse (e.g., drawdown in a vernal pool), males develop from some of the eggs, and instead of reproducing asexually, females produce eggs that require fertilization, but are also encased in a hard structure that is resistant to drought and adverse conditions. This is called an ephippium. After adverse conditions have passed, and under appropriate conditions (e.g., inundation of a dry vernal pool basin), ephippia hatch with an endowment of increased and novel genetic variability that is otherwise constrained under stable, favorable conditions and parthenogenetic reproduction.
In addition to allowing Daphnia to persist through unfavorable conditions, it turns out that ephippia are well-suited as a dispersal mechanism since they are easily transported by wind, especially when they coat the basin of a dry pool. Thus, in the context of metapopulations, it is easy to comprehend the importance of smaller and more ephemeral pools as sources for colonizing new habitats and introducing new genotypes into established populations, as shown by Altermatt and Ebert. Larger and more permanent pools tend to sustain themselves nicely, but they do less in the way of interacting demographically or genetically with other pools. This contrasts with an assumption common to many metapopulation models in which bigger patches with larger populations tend to be the sources for dispersing individuals.
The authors admit that there is little in the way of conservation concern for Daphnia magna, which is not rare nor is the species perceived to be negatively affected by limits to dispersal or genetic impoverishment. So far as I know this is the case for our Daphnia spp. as well. Given the unique reproductive modes of Daphnia, the extent to which this pattern can be generalized to other taxa may be limited, although the authors suggest similar dynamics may be found under environmental conditions that negatively affect local survival but benefit dispersal. But I liked this paper because it bolsters the argument that a pool can still have substantial ecological value even if it is tiny and temporary and not churning out amphibian metamorphs.
-Jim Arrigoni, SUNY-ESF
Altermatt F, Ebert D. 2010. Populations in small, ephemeral habitat patches may drive dynamics in a Daphnia magna metapopulation. Ecology 91: 2975-2982.
Daphnia are miniscule crustaceans that typically comprise a substantial fraction of the zooplankton in lentic freshwater systems throughout the world. They are a vital component of larval spotted salamander diet, particularly early in their development (see Joseph Freda's 1983 paper in Journal of Herpetology [vol. 17, pp. 177-179], "Diet of larval Ambystoma maculatum in New Jersey"). Daphnia are notable in that they employ multiple modes of reproduction, depending on their circumstances. When environmental conditions are favorable, females reproduce parthenogenetically -- they essentially clone themselves, which results in the production eggs that hatch into females. However, when environmental conditions take a turn for the worse (e.g., drawdown in a vernal pool), males develop from some of the eggs, and instead of reproducing asexually, females produce eggs that require fertilization, but are also encased in a hard structure that is resistant to drought and adverse conditions. This is called an ephippium. After adverse conditions have passed, and under appropriate conditions (e.g., inundation of a dry vernal pool basin), ephippia hatch with an endowment of increased and novel genetic variability that is otherwise constrained under stable, favorable conditions and parthenogenetic reproduction.
In addition to allowing Daphnia to persist through unfavorable conditions, it turns out that ephippia are well-suited as a dispersal mechanism since they are easily transported by wind, especially when they coat the basin of a dry pool. Thus, in the context of metapopulations, it is easy to comprehend the importance of smaller and more ephemeral pools as sources for colonizing new habitats and introducing new genotypes into established populations, as shown by Altermatt and Ebert. Larger and more permanent pools tend to sustain themselves nicely, but they do less in the way of interacting demographically or genetically with other pools. This contrasts with an assumption common to many metapopulation models in which bigger patches with larger populations tend to be the sources for dispersing individuals.
The authors admit that there is little in the way of conservation concern for Daphnia magna, which is not rare nor is the species perceived to be negatively affected by limits to dispersal or genetic impoverishment. So far as I know this is the case for our Daphnia spp. as well. Given the unique reproductive modes of Daphnia, the extent to which this pattern can be generalized to other taxa may be limited, although the authors suggest similar dynamics may be found under environmental conditions that negatively affect local survival but benefit dispersal. But I liked this paper because it bolsters the argument that a pool can still have substantial ecological value even if it is tiny and temporary and not churning out amphibian metamorphs.
-Jim Arrigoni, SUNY-ESF
Tuesday, October 19, 2010
What comes first - the alga or the egg?
Typically not long after learning about the incredible amphibian migrations to vernal pools in early spring, budding naturalists observe the egg masses of spotted salamanders and wood frogs taking on a dark green color. This is due to the growth of an alga, Oophila amblystomatis, we are told, which has colonized egg membranes and provides oxygen to the amphibian embryos while taking advantage of nitrogenous wastes. This tale of symbiosis adds another level of complexity to the saga of life in a vernal pool.
But it turns out the complexity might be profoundly greater. Dr. Ryan Kerney at Dalhousie University has reported algae within the embryonic cells of spotted salamanders; this discovery, if substantiated, would constitute the first known instance of an endosymbiotic relationship between a photosynthetic organism and a vertebrate. I eagerly await Dr. Kerney's formal publication, but in the meantime the news article spurred James Gibbs and me to consider what we might observe in any egg masses oviposited in the Heiberg pools this spring. Will algae "colonize" egg masses in the new pools, or would they require the assistance of dispersal vectors over varying periods of time? Digging through the literature on O. amblystomatis proved to be an unsatisfying experience, and an example of how conjecture can transform into widespread beliefs...
Although H. Orr is credited as the first to observe algae in spotted salamander egg membranes in an 1888 publication (widely cited but difficult to locate), it turns out that the alga species in question has never been formally described! Perry Gilbert in a 1942 paper describes how the name Oophila amblystomatis was informally adopted by F. D. Lambert ~30 years prior when distributing specimens to other researchers. Gilbert, at least, helps identification matters by providing extensive verbal descriptions, photographs, and illustrations of various forms of the alga, including non-motile and quadriflagellated forms. Gilbert also described experiments that strongly suggested that the pond water, not the parent, was the source provisioning algae to newly oviposited spotted salamander eggs. These results were corroborated by John Gatz with eggs of spotted salamanders, wood frogs, and Jefferson salamanders in a 1958 Journal of Herpetology note (7:137-138). Oddly, he cites an abstract from the 1969 Internation Botanical Congress by P. Biebel when offering the genus Chlamydomonas as a synonym for Oophila, but I cannot discern from the vague abstract how this is justified.
Additional key observations made by both Gilbert and Gatz are that among "several hundred" and "over a thousand" (respectively) spotted salamander egg masses observed in nature, each researcher recalled only a single instance of an egg mass lacking algae late in its development; the symbiosis appears to be nearly, but not completely, ubiquitous. Gilbert speculated that the egg mass lacking algae was located in an old stream bed, and so perhaps algae had been flushed from the system.
The failure of both Gilbert and Gatz to find algae within the reproductive tracts of female salamanders is in contrast to Kerney who supposedly found algae within adult salamander oviducts. This raises the possibility of vertical transmission of the symbiont, and that the salamanders themselves could be the vector bringing O. amblystomatis to novel habitats.
I wrote an email to Dr. Kerney last week to ask how he was dealing with the taxonomic impediments, and if he had any ecological insights regarding the colonization of O. ablystomatis in novel aquatic habitats such as the newly constructed pools at Heiberg. He replied that he has phylogenetic data that places "[their] local Oophila amblystomatis" in the Order Chlamydomonadales. Unfortunately, his research team lacks the resources to undertake more comprehensive phylogeographic analysis, but he speculated that a diversity of algal symbiont types could be associated with different salamanders. He added that it did not appear similar to any especially common northeastern species. In addition, Dr. Kerney confirmed that despite the strong evidence that O. amblystomatis is present in pond water and quickly colonizes newly deposited amphibian eggs, it has never been observed in a free-living state. He expressed a hunch that both vertical and horizontal algal acquisition might be at work, but resolving this experimentally has not been, nor will be, an easy task.
So, given some degree of cooperation by (or manipulation of!) reproductive spotted salamanders and wood frogs, we are poised to make some potentially interesting observations in our experimental system regarding the ecology of O. amblystomatis, with implications for the restoration of populations of amphibian species that enjoy the benefits of association with this ill-known alga(e?). James, Kim and I are in the initial phases of brainstorming experimental approaches to discerning vectors or reservoirs of O. amblystomatis. I wonder if any of the USC folks in the field have observed the tell-tale green egg masses in newly constructed pools down south, and within what kind of timeframes following construction?
This is to say nothing of the recently reported radical endosymbiosis, or what physiological titans spotted salamanders might become if they did not whisk themselves underground the first chance they get after metamorphosing....
Jim Arrigoni, SUNY-ESF
But it turns out the complexity might be profoundly greater. Dr. Ryan Kerney at Dalhousie University has reported algae within the embryonic cells of spotted salamanders; this discovery, if substantiated, would constitute the first known instance of an endosymbiotic relationship between a photosynthetic organism and a vertebrate. I eagerly await Dr. Kerney's formal publication, but in the meantime the news article spurred James Gibbs and me to consider what we might observe in any egg masses oviposited in the Heiberg pools this spring. Will algae "colonize" egg masses in the new pools, or would they require the assistance of dispersal vectors over varying periods of time? Digging through the literature on O. amblystomatis proved to be an unsatisfying experience, and an example of how conjecture can transform into widespread beliefs...
Although H. Orr is credited as the first to observe algae in spotted salamander egg membranes in an 1888 publication (widely cited but difficult to locate), it turns out that the alga species in question has never been formally described! Perry Gilbert in a 1942 paper describes how the name Oophila amblystomatis was informally adopted by F. D. Lambert ~30 years prior when distributing specimens to other researchers. Gilbert, at least, helps identification matters by providing extensive verbal descriptions, photographs, and illustrations of various forms of the alga, including non-motile and quadriflagellated forms. Gilbert also described experiments that strongly suggested that the pond water, not the parent, was the source provisioning algae to newly oviposited spotted salamander eggs. These results were corroborated by John Gatz with eggs of spotted salamanders, wood frogs, and Jefferson salamanders in a 1958 Journal of Herpetology note (7:137-138). Oddly, he cites an abstract from the 1969 Internation Botanical Congress by P. Biebel when offering the genus Chlamydomonas as a synonym for Oophila, but I cannot discern from the vague abstract how this is justified.
Additional key observations made by both Gilbert and Gatz are that among "several hundred" and "over a thousand" (respectively) spotted salamander egg masses observed in nature, each researcher recalled only a single instance of an egg mass lacking algae late in its development; the symbiosis appears to be nearly, but not completely, ubiquitous. Gilbert speculated that the egg mass lacking algae was located in an old stream bed, and so perhaps algae had been flushed from the system.
The failure of both Gilbert and Gatz to find algae within the reproductive tracts of female salamanders is in contrast to Kerney who supposedly found algae within adult salamander oviducts. This raises the possibility of vertical transmission of the symbiont, and that the salamanders themselves could be the vector bringing O. amblystomatis to novel habitats.
I wrote an email to Dr. Kerney last week to ask how he was dealing with the taxonomic impediments, and if he had any ecological insights regarding the colonization of O. ablystomatis in novel aquatic habitats such as the newly constructed pools at Heiberg. He replied that he has phylogenetic data that places "[their] local Oophila amblystomatis" in the Order Chlamydomonadales. Unfortunately, his research team lacks the resources to undertake more comprehensive phylogeographic analysis, but he speculated that a diversity of algal symbiont types could be associated with different salamanders. He added that it did not appear similar to any especially common northeastern species. In addition, Dr. Kerney confirmed that despite the strong evidence that O. amblystomatis is present in pond water and quickly colonizes newly deposited amphibian eggs, it has never been observed in a free-living state. He expressed a hunch that both vertical and horizontal algal acquisition might be at work, but resolving this experimentally has not been, nor will be, an easy task.
So, given some degree of cooperation by (or manipulation of!) reproductive spotted salamanders and wood frogs, we are poised to make some potentially interesting observations in our experimental system regarding the ecology of O. amblystomatis, with implications for the restoration of populations of amphibian species that enjoy the benefits of association with this ill-known alga(e?). James, Kim and I are in the initial phases of brainstorming experimental approaches to discerning vectors or reservoirs of O. amblystomatis. I wonder if any of the USC folks in the field have observed the tell-tale green egg masses in newly constructed pools down south, and within what kind of timeframes following construction?
This is to say nothing of the recently reported radical endosymbiosis, or what physiological titans spotted salamanders might become if they did not whisk themselves underground the first chance they get after metamorphosing....
Jim Arrigoni, SUNY-ESF
Monday, October 11, 2010
New paper on vernal pool amphibian and macroinvertebrate detection probabilities
Annie Curtis and Dr. Peter Paton at the University of Rhode Island have just published a paper titled "Assessing detection probabilities of larval amphibians and macroinvertebrates in isolated ponds" in the journal Wetlands. Although they describe the utility of their results within the framework of monitoring the ecological condition of isolated aquatic habitats such as vernal pools based on observations in 36 Rhode Island ponds, there are clear implications for my ambition to document community assembly in the Heiberg constructed pools. Curtis and Paton add a great deal of temporal resolution to the general phenological patterns described in the seminal paper by Wiggins et al. in 1980, "Evolutionary and ecological strategies of animals in annual temporary pools." The waxing and waning of detection probabilities for 8 amphibian species and 10 macroinvertebrate families between mid-May and the end of July are nicely portrayed in Figures 2 and 3. Also, the influence (or lack thereof) on detection probabilities of abiotic and habitat structure variables such as water temperature, pond depth, aquatic vegetation, and woody debris are instructive for designing a sampling protocol in the present and as habitat develops in the future.
-Jim Arrigoni, SUNY-ESF
-Jim Arrigoni, SUNY-ESF
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