Ostracod distribution

Schoepfle Garden Erie County, Ohio 3-08-2017

Two days ago I came across Candona truncata in a temporary pool in Lorain County Ohio. This is the only time this species has been found in either Lorain County or Erie County with about 100 pools having been sampled covering an area of about 400 Sq. miles. About 60 miles away (about 100 kilometers) C. truncata is found in Geauga county. The two areas could not be more different. Lorain and Erie county are in the Great Lakes plains and Geauga county is in the foothills of the Appalachian mountains.

So discussing this we arrived at three possible explanations for the spotty distribution since so many pools have been sampled in Lorain and Erie county.

1) Pure chance, a bird, let us say, chance to land at a pool with this species and carried it to this one particular pool.

2) The waters of this pool in Erie county is the only one with the environmental conditions allowing the ostracod to thrive. A further note the Erie county pool lies in a floodplain of a river the Geauga pool does not.

3) these two pools are of the same geologic age and have escape changes that have occurred to other pools.

These are the best Ideas we could come up with and considering that this distribution question must have occurred many times in the study of ostracods we were wondering what the consensus is to the cause of these odd distributions.

John Lavelle

The other ostracods found in the same sample.

1) top Candona elliptica bottom Candona decora

2) top Candona crogmaniana bottom Candona (distincta ?)

1 2 3

upper C. crogmaniana lower C. truncata

4

top Bradleystrandesia tincta lower ?????

5 6

Below is the temporary pool in Geauga county Ohio that Candona truncata was found.

7) upper C. truncata lower C. exculpta

7

8) upper Candona candida lower right C. decora

9) top C. exculpta bottom Candona punctate

10) top Candona fossulensis bottom Cyclocypris ampla

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Chris GOURAMANIS (Asst. Prof.):

Department of Geography, Faculty of Arts and Social Sciences, National University of Singapore,

Interesting question, and one I've been pondering for Australian ostracod species distributions for a while. So speaking from an Australian ostracod distribution perspective, each of the mechanisms that you have proposed are viable explanations for the presence of C. truncata in your lake. However, I wouldn't treat these alternatives as end members, and it could quite easily be a combination of all three explanations + a few others (see below). And so each occurrence of a species in a lake would be due to a unique culmination of factors and luck.

Desiccation or dormant eggs may also have been deposited in the system from previous populations that may locally have disappeared. I don't know this species and if it does produce eggs that can remain dormant - happy to be educated on that point. Desiccation resistant eggs can also be mobilised by wind or river flooding (this may be an exceptional case for Australian rivers connecting wetlands during flooding events and disconnecting during dry periods).

A few questions to ponder are:

Whether your community has males and females?

Is there a difference in predators/pathogens between sites?

Could the species have occurred but not sampled in intermediate sites, i.e. different micro-habitat within a lake or just simply plain sampling bad luck (Unlikely but it does happen)?

Have you considered collecting a sediment core and seeing if there are C. truncata valves preserved in earlier time periods from this lake? That may shed some light on whether the occurrence of this species today has corollaries in the past.

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Dave Horne Professor of Micropalaeontology

School of Geography Queen Mary, University of London

Interesting observation! I have encountered similar puzzles. The most extreme, perhaps, was an abundance of Heterocypris incongruens in a temporary puddle on a dirt track, while on the same day a shallow ditch at the side of the track only a couple of metres contained several other ostracod species but no H. incongruens.

I think your explanations (1) and (2) are the most likely, possibly in combination as Chris has suggested. I would speculate that this species most likely has resting eggs (but note that whole individuals can also be transported by birds etc.), and if there were no males then maybe these were parthenogenetic populations, in which case it only takes the transport of a single egg or an individual ostracod into the pond to start a new population. One other (speculative!) solution might be some form of competitive exclusion; perhaps, for example, there is another species (not necessarily an ostracod) that gets into these ponds and eats the eggs or small juveniles of C. truncata, so that the success of the ostracod depends on the absence of another species.

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Robin James Smith

Lake Biwa Museum Japan

It’s not only birds that are known to disperse micro-fauna. Large mammals and amphibians play a role too. In forested areas where wading birds are not common, mammals could be the most important dispersers.

Any evidence of large animal activity around that particular pool? e.g. footprints.

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Dr. Francesc Mesquita-Joanes

Ecologia, Fac. Biologia, Univ. Valencia

In addition to the wise comments of Okan, Chris, Dave and Rob, I would like to comment on this issue, which I find fascinating.

It’s quite clear to me that if birds or mammals can connect two sites, ostracods can be transported (mostly those with diapausing eggs, but not only). But now, we can consider also humans, and then ostracods can go almost anywhere. Rob mentioned a short note we published on this human transport of ostracods, which is an example of a huge distance. But there are others at shorter distances like these:

Valls, L., Castillo-Escrivà, A., Mesquita-Joanes, F., Armengol, X., 2016. Human mediated-dispersal of aquatic invertebrates with waterproof footwear. Ambio 45(1), 99-109

Waterkeyn, A., B. Vanschoenwinkel, S. Elsen, M. Anton-Pardo, P.Grillas, and L. Brendonck. 2010. Unintentional dispersal of aquatic invertebrates via footwear and motor vehicles in a Mediterranean wetland area. Aquatic Conservation: Marine and Freshwater Ecosystems 20: 580–587.

Once they arrive there, as already said by my colleagues, they could survive or not depending on conditions, reproduce or not depending also on their type of reproduction or if adult females arrived with eggs... But to occupy the habitat, it depends not only on appropriate abiotic conditions (maybe they are adapted at a shorter hydroperiod in that particular pond compared to others around, maybe it’s a bit more acidic or salty than others..), but also, and importantly, on previous organisms occupying (or not) the pond, including algal food, potential predators or competitors (particularly in small, restricted habitats like a temporary pond). Regarding competitors, such as other ostracod species in ponds around that you mentioned, there is the so-called “priority effects”, so that the one that arrives first to the pond, can become occupying that pond (first come, first served), even if there is another ostracod species arriving later with slightly better adaptations (it may take a while, many years or maybe it never happens, that the newcomer replaces the old guy occupying the pond).

About priority effects and contingency (in general and in ostracods), you can have a look here:

Castillo-Escrivà, A.; L. Valls; C. Rochera; A. Camacho; F. Mesquita-Joanes (2017) Disentangling environmental, spatial and historical effects on ostracod communities in shallow lakes. Hydrobiologia 787 (1): 61–72 .

Castillo-Escrivà, A.; L. Valls; C. Rochera; A. Camacho; F. Mesquita-Joanes (2017) Metacommunity dynamics of Ostracoda in temporary lakes: overall strong niche effects except at the onset of the flooding period. Limnologica 62: 104–110.

De Meester, L., A. Go´mez, B. Okamura & K. Schwenk, 2002. The monopolization hypothesis and the dispersal–gene flow paradox in aquatic organisms. Acta Oecologica 23: 121–135

Fukami, T., 2015. Historical contingency in community assembly: integrating niches, species pools, and priority effects. Annual Review of Ecology, Evolution, and Systematics 46: 1–23

Louette, G. & L. De Meester, 2007. Predation and priority effects in experimental zooplankton communities. Oikos 116: 419–426.

So, there are a lot of possibilities, related to dispersal, adaptation, disturbances... Part of it might be deterministic (e.g. to have adaptations to particular conditions), but also much chance could be influencing what you find (e.g. a bird stopped there to drink on its way somewhere else and left a dropping there). Ostracods are excellent for research in this topic, as we can check what was present before using the valve remains, as Chris suggested, and as we did in one of the papers cited above. Hope this helps.

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Dr. Alison J. Smith, Professor

Department of Geology Kent State University

Hi John, well this a great discussion! Candona truncata is a minor member of the "Great Lakes fauna" in the modern ostracode distributions, and is found sporadically from New York all the way over through forested Minnesota, and during the early Holocene, westward into the eastern Dakotas. Generally, it maps around the North American Great Lakes, and in the forested regions in particular. These comments on competitive exclusion, first arrivals, and vectors for introduction are all important here.

Ostracode distributions within forested regions are particularly puzzling. Many of us have found small ponds, springs, vernals, in the forest, not so easy to get to by birds, maybe more easily found by amphibians and other small animal vectors. These forest springs/pools are often close together yet have quite different ostracode fauna, and with just about identical water chemistry and physical characteristics. So, is it first come, first serve? Is it competitive exclusion? Once there, are the populations persisting in stable springs for very long periods of time? The species does not appear to undergo a torpid phase or have desiccation-proof eggs, but frankly no one has really set up the experiments. Also, we don't know where the species spends its time from egg through juvenile to adult. To me when I find Candona truncata in Holocene or Pleistocene cores, its a lovely ecological signal of forested landscapes with fresh, bicarbonate enriched water, if a lake, typically marl producing, conditions that often no longer exist at the core site! Lots of questions.

Its associated ostracodes often include Candona distincta, Candona decora, and Candona punctata, and sometimes Candona candida (the latter not so common in North America as in Europe) which prefer the same environmental conditions.

Regionally, birds play a role because the distributions overlap with the major flyways for the Great Lakes, but occupation and continuence in individual ponds, vernals, and springs...that is a continuing question.

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Prof Dr Koen Martens

Royal Belgian Institute of Natural Sciences (RBINS)

another ostracod dispersal story can be found in:

SCHÖN, I., SHEARN, R., K. MARTENS, A. KOENDERS & S.A. HALSE 2015. Age and

origin of Australian* Bennelongia* (Crustacea, Ostracoda). Hydrobiologia

750: 125-146.

There are many different stories about "aberrant" ostracod distributions,both at short and longer ranges. While sampling an area with many rockpools

in Mongolia in 2005, I found a large population of Heterocypris in one pool, while an identical (size, chemistry, temp,..) pool 2 m away was

devoid of any ostracods. Eucypris virens in a winter species in Western Europe, but I found a healthy population in the middle of summer (August)

in Belgium. Etc.

I put most value on the monopolisation hypothesis that Paco brought up,although I do realize that it will not explain all "strange" occurrences.

As Steven J Gould argued for a long time, "chance" is an underestimated

force in evolution. I think also in Ecology...

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Burkhard Scharf

there is also an other possible explanation: At the beginning of work with ostracods I have collectected in Greece at a sample site with many Cyprideis torosa. The next sample that I have taken was in Germany and I have found few of Cyprideis torosa, dead. Explanation. I did not have cleaned enough the net. Since that time I have cleaned very carefully the net!

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Radovan Kyska Pipik Head of Department

EARTH SCIENCE INSTITUTE Slovak Academy of Sciences

I have similar observation from marsh in front of the travertine dome. There are several holes of the size 1 m2, more than 1 m depth and fed by subterranean water, but only one of these holes was rich on species (13 species) and only in this one hole we found Vestalenula.

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John Lavelle

A couple of quick points.

Professor Home puzzle concerning Heterocypris incongruens is one I encounter. My bird bath is home to a colony of these small ostracods and they appear to come from a small pool in the park across the street from where I live (30 to 40 meters away). Considering how quickly this species is able to disperse one of the big surprises is that this ostracod is found almost no where else in the two counties. Most of my sampling is down in deep woods and it make me wonder if this species has either adapted to or already had the traits to exploit human changes to the environment. Interestingly, to me anyways, is that there is a species of cladoceran that also maybe suited to human changes to the environment. This is the species Moina which I find in areas recently cleared but is rare in almost all other area. Professor Hann of the University of Mantoba has also found this species able to inhabitant water in tires and old tin cans.

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Several of the respondents brought up the issue of predation. What is interesting is that in at least the area sampled all the Candona species are overwhelmingly found in the winter and early spring months, many times under ice cover, and they mostly disappear before most animals appear in the pools. The ice cover also perhaps protects them from birds.

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Professor Home again: "One other (speculative!) solution might be some form of competitive exclusion; perhaps, for example, there is another species (not necessarily an ostracod) that gets into these ponds and eats the eggs or small juveniles of C. truncata, so that the success of the ostracod depends on the absence of another species."

This has the problem that 4 other species of Candona can be found at the same time which would mean that the predator would have to be species specific.

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Robin Smith asked if any mammals are found in the area that could be transporting the ostracods. Yes deers, raccoons and especially squirrels are common.

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