Clownfish larva cognition and learning

[ThRoewer]

Got a new book: Fish Cognition and Behavior.
Quite interesting and from the bits I've read so far fish are not as simple minded as many may think. Their brains are capable of quite some tasks and some have incredible long term memory.
They also have clearly individual personalities.

It turns out that many reef fish larva - among them clownfish larva - usually stay close and settle near their birth site/reef. Genetic sampling has shown this.
It also seems the larva learn the chemical signature of their parents anemone species while still in the egg and look for this when settling down.
Another suspicion is that they actually memorize the sounds of their home reef and use that to make sure to settle close to home. This is currently under investigation.

To me this explains a lot.
For example why many tank bred clowns are not so conditioned to certain anemones but are a bit more flexible. It may also explain why some have a hard time getting the idea of going into an anemone in the first place. They never learned it.

To me this has quite a few consequences. For once I will try to keep my brodstock pairs in the right kind of anemones.

 

[ExpertMarine]

Interesting.

 

[DasCamel]

Very cool. Post more tid bits!

 

[CoralsAddiction]

This study assumes that fish fry stay at their birth site and don't get carried away from it by the ocean current?

 

[ThRoewer]

It does not assume but rater found genetic evidence that this is actually the case.
I think ocean currents are vastly overestimated in clownfish larva dispersal and most larva keep on the land side of the reef where they will not be that easy carried off into the open ocean. You will actually find a lot of reef and even open water fish larva and young fish in mangrove areas and bays that are protected from the currents.
A clownfish larva that gets carried off into the open ocean is likely to perish. The chances to find another reef are actually pretty small. Also keep in mind that the anemones clownfish populate are predominantly on the inner reefs or even in the tidal area.
I would go so far to say that the hatching of the eggs is timed to coincide with rising tide to give the larva a better chance.
Local varieties like the Darwin ocellaris are also a confirmation of this.

Also if you ever have observed how fast and enduring clownfish larva can actually swim you know that it is not impossible for them to stay within a certain area. I had them in round tanks and they could beat any flow I throw at them.

Now, this doesn't mean some larva get carried away and may land on some other reefs but the distribution areas of the different clownfish species shows that this is not happening very often. Also localized island populations could not exist if their larva get carried away in the currents.

And this does not only apply to clownfish but to a large number of reef fish.

 

[ThRoewer]

Some interesting research on Amphiprion percula larva dispersal:

Larval dispersal connects fish populations in a network of marine protected areas

Abstract
Networks of no-take marine protected areas (MPAs) have been widely advocated for the conservation of marine biodiversity. But for MPA networks to be successful in protecting marine populations, individual MPAs must be self-sustaining or adequately connected to other MPAs via dispersal. For marine species with a dispersive larval stage, populations within MPAs require either the return of settlement-stage larvae to their natal reserve or connectivity among reserves at the spatial scales at which MPA networks are implemented. To date, larvae have not been tracked when dispersing from one MPA to another, and the relative magnitude of local retention and connectivity among MPAs remains unknown. Here we use DNA parentage analysis to provide the first direct estimates of connectivity of a marine fish, the orange clownfish (Amphiprion percula), in a proposed network of marine reserves in Kimbe Bay, Papua New Guinea. Approximately 40% of A. percula larvae settling into anemones in an island MPA at 2 different times were derived from parents resident in the reserve. We also located juveniles spawned by Kimbe Island residents that had dispersed as far as 35 km to other proposed MPAs, the longest distance that marine larvae have been directly tracked. These dispersers accounted for up to 10% of the recruitment in the adjacent MPAs. Our findings suggest that MPA networks can function to sustain resident populations both by local replenishment and through larval dispersal from other reserves. More generally, DNA parentage analysis provides a direct method for measuring larval dispersal for other marine organisms.


Persistence of self-recruitment and patterns of larval connectivity in a marine protected area network

Abstract
The use of marine protected area (MPA) networks to sustain fisheries and conserve biodiversity is predicated on two critical yet rarely tested assumptions. Individual MPAs must produce sufficient larvae that settle within that reserve's boundaries to maintain local populations while simultaneously supplying larvae to other MPA nodes in the network that might otherwise suffer local extinction. Here, we use genetic parentage analysis to demonstrate that patterns of self-recruitment of two reef fishes (Amphiprion percula and Chaetodon vagabundus) in an MPA in Kimbe Bay, Papua New Guinea, were remarkably consistent over several years. However, dispersal from this reserve to two other nodes in an MPA network varied between species and through time. The stability of our estimates of self-recruitment suggests that even small MPAs may be self-sustaining. However, our results caution against applying optimization strategies to MPA network design without accounting for variable connectivity among species and over time.


Are clownfish groups composed of close relatives? An analysis of microsatellite DNA variation in Amphiprion percula

Abstract
A central question of evolutionary ecology is: why do animals live in groups? Answering this question requires that the costs and benefits of group living are measured from the perspective of each individual in the group. This, in turn, requires that the group's genetic structure is elucidated, because genetic relatedness can modulate the individuals' costs and benefits. The clown anemonefish, Amphiprion percula, lives in groups composed of a breeding pair and zero to four nonbreeders. Both breeders and nonbreeders stand to gain by associating with relatives: breeders might prefer to tolerate nonbreeders that are relatives because there is little chance that relatives will survive to breed elsewhere; nonbreeders might prefer to associate with breeders that are relatives because of the potential to accrue indirect genetic benefits by enhancing anemone and, consequently, breeder fitness. Given the potential benefits of associating with relatives, we use microsatellite loci to investigate whether or not individuals within groups of A. percula are related. We develop seven polymorphic microsatellite loci, with a number of alleles (range 2"“24) and an observed level of heterozygosity (mean = 0.5936) sufficient to assess fine-scale genetic structure. The mean coefficient of relatedness among group members is 0.00 ± 0.10 (n = 9 groups), and there are no surprising patterns in the distribution of pairwise relatedness. We conclude that A. percula live in groups of unrelated individuals. This study lays the foundation for further investigations of behavioural, population and community ecology of anemonefishes which are emerging as model systems for evolutionary ecology in the marine environment.

 

[ThRoewer]

some more:

Probability of successful larval dispersal declines fivefold over 1 km in a coral reef fish

Abstract
A central question of marine ecology is, how far do larvae disperse? Coupled biophysical models predict that the probability of successful dispersal declines as a function of distance between populations. Estimates of genetic isolation-by-distance and self-recruitment provide indirect support for this prediction. Here, we conduct the first direct test of this prediction, using data from the well-studied system of clown anemonefish (Amphiprion percula) at Kimbe Island, in Papua New Guinea. Amphiprion percula live in small breeding groups that inhabit sea anemones. These groups can be thought of as populations within a metapopulation. We use the x- and y-coordinates of each anemone to determine the expected distribution of dispersal distances (the distribution of distances between each and every population in the metapopulation). We use parentage analyses to trace recruits back to parents and determine the observed distribution of dispersal distances. Then, we employ a logistic model to (i) compare the observed and expected dispersal distance distributions and (ii) determine the relationship between the probability of successful dispersal and the distance between populations. The observed and expected dispersal distance distributions are significantly different (p < 0.0001). Remarkably, the probability of successful dispersal between populations decreases fivefold over 1 km. This study provides a framework for quantitative investigations of larval dispersal that can be applied to other species. Further, the approach facilitates testing biological and physical hypotheses for the factors influencing larval dispersal in unison, which will advance our understanding of marine population connectivity.


This one is on A. clarkii:
USING ISOLATION BY DISTANCE AND EFFECTIVE DENSITY TO ESTIMATE DISPERSAL SCALES IN ANEMONEFISH

Abstract
Robust estimates of dispersal are critical for understanding population dynamics and local adaptation, as well as for successful spatial management. Genetic isolation by distance patterns hold clues to dispersal, but understanding these patterns quantitatively has been complicated by uncertainty in effective density. In this study, we genotyped populations of a coral reef fish (Amphiprion clarkii) at 13 microsatellite loci to uncover fine-scale isolation by distance patterns in two replicate transects. Temporal changes in allele frequencies between generations suggested that effective densities in these populations are 4"“21 adults/km. A separate estimate from census densities suggested that effective densities may be as high as 82"“178 adults/km. Applying these effective densities with isolation by distance theory suggested that larval dispersal kernels in A. clarkii had a spread near 11 km (4"“27 km). These kernels predicted low fractions of self-recruitment in continuous habitats, but the same kernels were consistent with previously reported, high self-recruitment fractions (40"“60%) when realistic levels of habitat patchiness were considered. Our results suggested that ecologically relevant larval dispersal can be estimated with widely available genetic methods when effective density is measured carefully through cohort sampling and ecological censuses, and that self-recruitment studies should be interpreted in light of habitat patchiness.