Hier ist ein interessanter Artikel der argentinischen Freunde, Felipe Alonso und Pablo Calvino über saisonelle Killis. Er hat mir freundlicher weise eine englische Version geschickt. Der original Artikel ist als PDF zum runterladen, siehe Link.



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Felipe Alonso
BRIEF COMMUNICATION

Seasonal killis in permanent waters (Cyprinodontiformes)

Authors

Felipe Alonso1,2 *, Pablo Calviño1
1 Killis Research and Conservation Group (GICK), 2 NOA Bioethics and Geosciences Institute (IBIGEO) - CONICET. * felipealonso@gmail.com

Annual fish, or better called "seasonal", since many can have more than one cycle in a year (Costa, 2002, Alonso et al., 2016) or not completely regular cycles that can extend for more than a year, present a series of adaptations that allow them to live in ephemeral aquatic environments, which usually dry out completely during a part of the year (Berois at al., 2015). However, the presence of seasonal fish in permanent aquatic environments, such as rivers and lagoons, could be more frequent than might be assumed a priori. Through a series of occasional observations we have been able to confirm that it is not so rare to find these species in permanent water environments. In this brief note we comment on some of these cases and briefly discuss some evolutionary and ecological implications of the use of permanent environments by seasonal fish.

Figure 1. Austrolebias alexandri, top female, down male.
Some studies have emphasized the relationship between the connectivity between seasonal pools (or degree of isolation) and the dispersal capacity of species as an important factor structuring the composition of species (Loureiro et al., 2015) . In a work by Borthagaray et al. (2015), for example, found that the persistence of large species depends on the degree of connectivity of the puddles. Cunillera-Montcusí et al., (2017) evaluated a pond system in the Pyrenees and one of its conclusions is that the presence of species with low dispersal capacity is limited by the degree of isolation of the puddles.

Below I will list some of the records we have made of seasonal killifish in permanent waters. We have two very different situations: 1) The presence of seasonal species in permanent waters due to floods (more frequent) and 2) the presence of seasonal species in permanent waters in a more stable manner, not the product of floods.
Let's start then with the cases that we could attribute to some type of flood and subsequent colonization or occasional presence in permanent waters. Here, we can mention a record of Austrolebias bellottii (Steindachner 1881) in 2012 on the Gualeguay river margin, on provincial route 12, south of the province of Entre Ríos. The specimens were in an area flooded by the river along with permanent water species (Corydoras longipinnis Knaack, Astyanax spp, etc.), apparently the specimens would come from nearby marshes that were in contact with the river because of the flood. This case could be framed within a possible sporadic use of the puddle, possibly during this type of flood, some specimens are dispersed through the river and allow the genetic flow between puddles and the colonization of new environments. A similar case is observed with Austrolebias alexandri (Castello and López 1974) (Fig. 1) in the marshes of the Concepción River south of Concordia, Entre Ríos. In a lagoon adjacent to Route 14 that was connected to the Concepción River (Fig. 2) we were able to collect abundant specimens of A. alexandri in one of its margins, while in the central part of the lagoon there was a large number of fish from waters permanent (Astyanax spp., Hyphessobrycon spp., Cichlasoma dimerus, Australoheros facetus, etc.) and even specimens more than 20 cm long of fish-eating species such as Hoplias malabaricus and Crenicichla lepidota. In this case, it would also probably be the connection of a temporary environment with one of permanent waters in a flood episode. It is interesting that in this case we did not find specimens of A. alexandri outside the area where the temporary puddle may have been, which we later corroborated on another trip. This difference in the spatial distribution observed between the mentioned cases of A. alexandri and A. bellottii, is possibly reflecting the different dispersal capacity of these species in permanent waters. Vaz Ferreira et al. (1966) already mentions the eventual connection of seasonal pools with permanent water environments ("troughs, streams" and "rivers") during periods of flooding and the presence of these species in these environments and discusses the exchange of fauna between seasonal environments and permanent. It is interesting that in this discussion there is implicit a gradation in the degree of seasonality of the puddles that is also relevant when considering the biology of these species. That is, deepening this concept, not only is the connectivity of the puddles important, but also how ephemeral they are and with what they connect, that is, if they connect with other ephemeral environments (how ephemeral they are?) Or permanent environments, lagoons. , rivers, etc. It would be interesting to evaluate in future studies the influence of these aspects in the composition of species. In our experience and based on occasional non-systematized observations we have observed that apparently these factors could be very important when determining the composition of seasonal killifish species of the puddles of the Chaco Pampa plain.

Figure 2. Permanent lagoon connected to a stream, near Concordia, Entre Ríos. Austrolebias alexandri were collected in a margin of the lagoon. Probably three different environments (a seasonal puddle, a lagoon and a river) are connected during the highest levels.
Returning to the examples that we mentioned, we have other cases in which seasonal species are observed in permanent waters without there being evidence that this is the product of floods. Perhaps these are the most unexpected and interesting examples. For example, in 2012 we found Pterolebias longininis Garman 1895 in the main channel of a tributary stream of the Río de Oro, in the province of Chaco (Figs 3-4), along with many species of permanent waters.

Figure 3. Affluent stream of the Río de Oro, Province of Chaco. Permanent aquatic environment and running water where abundant Pterolebias longipinnis were recorded, along with Astyanax lacustris, Aphyocharax anisitsi and other typical species of permanent environments.

Figure 4. Pterolebias longipinnis, from Río de Oro, Chaco.
Also in Entre Ríos, near the town of dunes we have observed a permanent population of Austrolebis nigripinnis Regan and A. bellottii in a large lagoon whose central zone has permanent waters but has a large marginal area that dries completely during part of the year . When the lagoon grows the marginal zone fills with water and the Austrolebias hatch.
Juan Manuel Palacios, (pers. Pers.) In 1995, observed the presence of Austrolebias bellottii and A. elongatus in the Pescado stream, Otamendi, province of Buenos Aires, after a terrible storm and subsequent flood. Casciotta et al. (1999) collected a specimen of A. robustus in the Arroyo La Nutria Mansa, province of Buenos Aires, which we later determined as that species. These observations, added to the fact that the same species is usually found along both banks of a river, are conclusive evidence of this mechanism of dispersion.

Something similar we have observed in some cases in the zone of the humid pampa with Austrolebias elongatus in permanent lagoons, where apparently this species would realize its cycle depositing its eggs in the marginal zones of the lagoon. This has also been observed by Jorge Osvaldo Fernández Santos (pers. Comm.) In lagoons of the province of Buenos Aires and also by Agustín Villanucci (pers. Comm.) In a lagoon in the southeast of Entre Ríos.

It is also common to find this species in rivers with permanent waters, in different forums of fishermen we have found that it is common to fish with Austrolebic canes elongatus (Steindachner 1881) in these environments (Fig. 5). This gives us the guideline that there are species with a greater tendency to live, colonize or disperse in this type of environment.
It is likely that the ability of certain species to use or live in permanent aquatic environments is a key factor in the evolution of them, since it allows them to take advantage of other resources, for example in the case of the Austrolebias elongatus would allow them to prey on others fishes.

Another interesting question is the relationship between the amplitude of the geographical distribution and the dispersal capacity of the species. Just Pterolebias longipinnis is one of the species of Rivulidae with greater geographical distribution (Costa, 2005) and is a species that we have collected many times in semi-permanent or permanent aquatic environments. It is possible that the ability to live in aquatic environments of these characteristics is also related to the ability of this species to disperse, something that, for example, we have also observed in Austrolebias bellottii, which coincidentally is also a species with a very large geographical distribution. .

Figure 5. Male of Austrolebias elongatus from Arroyo El Hueso, in the town of Azul, Buenos Aires. Fish with cane using bait worm. Photo: Sebastián Gómez
In conclusion, although these species have adaptations to life in ephemeral aquatic environments and require the drying of their environment (or part of it) for their development, we see that they can live at least part of their lives in permanent aquatic environments or even such once they can complete a complete cycle by depositing their eggs on the margins of rivers or lagoons. How common is this and the evolutionary and ecological implications of these issues remains to be seen in future studies that delve into this. Our intention with this contribution is to make this phenomenon visible so that they can be taken into account in future works based on more systematized observations.
Thanks
To Sebastián Gómez for providing the copy of Austrolebias elongatus of Arroyo el Hueso, photos and data on the subject.
Material examined
Austrolebias elongatus (Steindachner, 1881). IBIGEO-I 457, 1, 97mm, Arroyo El Hueso, Azul, Buenos Aires, 36 ° 43'56.56 "S, 59 ° 48'44.55" W