Why do several species of minnows breed over the same nest?

For those unaware, I was on a brief hiatus to the Joint Meeting of Ichthyologists and Herpetologists annual meeting in Chatanooga, TN! There were numerous exciting talks, especially those pertaining to minnows, and it seems in the near future, there may be some resolution of the systematics of minnows, suckers, and loaches (see Part III of my first post if you think we understand the systematics of this group!). Stay tuned as I will update the blog as new studies are published!

One of the many amazing things about Tennessee relative to Oklahoma (where I currently live) is the clarity of the water. In Oklahoma, water clarity is extremely low (due to high turbidity) throughout most of the state with the exception of systems to the east (e.g., the Blue River). In Tennessee, several of the rivers are cool and clear and provide unique snorkeling opportunities. If you jump in the waters in Tennessee in May or June, you may see HUGE aggregation of small fishes on top of a large gravel nest (Freshwaters Illustrated has some excellent pictures of nest associations). What is this? Aren’t individuals supposed to mate only with individuals from their species?

These large spawning aggregations are known as nest associations and are well documented in the scientific literature. Essentially, male Nocomis or Campostoma build nests by gathering small stones in their mouth and bring them back to a designated area for nest building — as a quick aside, minnows may also spawn over sunfish (Centrarchidae: Lepomis) nests. After building the nest for spawning, other minnows will come to these nests and spawn over the nest. By spawning over the nest, the eggs from these minnows are fertilized and fall into the nest of the Nocomis

What minnows may spawn over the nests of Nocomis? Frankly, the minnows documented to spawn over such nests are pretty diverse. Several species of Notropis spawn over nests although most of these species may be in the subgenus Hydrophlox (Cashner et al. 2011). Other species of Chrosomus, Dionda, Lythrurus, Luxilus, Notemigonus, Notropis, and even Cyprinella – a crevice spawner – have been documented as nest associates (Shao 1997; Cashner and Bart 2010; Phillips et al. 2011Mattingly and Black 2013). I think this is representative of the minnows that are nest associates, but this list is unlikely to include all species that are actual nest associates. What do all these species have in common? They have demersal eggs which sink to the substrate so that they can be protected by the host male. Other species, such as those with pelagic eggs (e.g., Hybognathus amarus) or those that guard their eggs (e.g., Pimephales spp.), have life-history traits that prevent them from taking advantage of nest associations. 

As an evolutionary biologist, one of the more intriguing questions is: how have nest associations evolved? Step out of your human mindset and remind yourself that evolutionary speaking, every organism’s goal is to pass on their genes such that their offspring will reproduce in the future and pass on their genes (and so on). One may expect that for these associations to evolve, they must benefit both species – i.e., they are mutualistic. Not surprisingly, several studies support this notion and find that both species benefit largely as a result of the dilution effect (Wallin 1992; Johnston 1994a; Johnston 1994b; Shao 1997). By not 1, but 2 or 3 or 4 species depositing their eggs in the same nest, the number of eggs in a nest increases significantly (potentially by several magnitudes depending on the species of nest associates). As a result, the chance of the eggs of the host species (e.g., Nocomis) being eaten in any particular predation event is reduced. The nest associates depositing their eggs in the host’s nest may suffer from increased predation, but benefit from the parental care they receive by the guarding male (Johnston 1994b).

Although more in-depth studies are needed, it does seem that some species may be nest associates more frequently than other species. In fact, minnow species that are “strong” nest associates of Nocomis have ranges largely overlapping with Nocomis species whereas “weak” nest associates don’t exhibit such a pattern (Pendleton et al. 2012). Further, “strong” nest associates were much more rare than “weak” nest associates. This relationship is worth a further look as it may have important implications for the loss of biodiversity – i.e., if we lose Nocomis, will we lose its “strong” nest associates? That may be too much of a generalization, but this is something certainly worth pondering and investigating.

So, the next time you are you in a nearby stream in mid-summer, grab a mask and snorkel and look underwater. Maybe you won’t see anything. Maybe you will see just a few fish swimming around. But maybe, just maybe, you will see a large conglomerate of minnows swimming around and spawning over the nest of a Nocomis, Campostoma, or Lepomis. Hopefully then, you will understand the true beauty of such nest associations!

References:

Cashner MF, and HL Bart Jr. 2010. Reproductive ecology of nest associates : use of RFLPs to identify cyprinid eggs. Copeia 2010(4):554-557.

Cashner, MF, KR Piller, and HL Bart Jr. 2011. Phylogenetic relationships of the North American subgenus HydrophloxMolecular Phylogenetics and Evolution 59(2011):725-735.

Johnston CE. 1994a. Nest association in fishes: evidence for mutualism. Behavioral Ecology and Sociobiology 35(6):379-383.

Johnson CE. 1994b. The benefit to some minnows of spawning in the nests of other species. Environmental Biology of Fishes 40(2):213-218.

Mattingly HT, and TR Black. 2013. Nest association and reproductive microhabitat of the threatened blackside dace, Chrosomus cumberlandensis. The Southeastern Naturalist 12(4):49-63.

Pendleton RM, JJ Pritt, BK Peoples, and EA Frimpong. 2012. The strength of Nocomis nest association contributes to patterns of rarity and commoness among New River, Virginia cyprinids. The American Midland Naturalist 168(1):202-217.

Phillips CT, RJ Gibson, and JN Fries. 2008. Spawning behavior and nest association by Dionda diabolii in the Devils River, Texas. The Southwestern Naturalist 56(1):108-112.

Shao B. 1997. Effects of golden shiner (Notemigonus crysoleucas) nest association on host pumpkinseeds (Lepomis gibbosus): evidence for a non-parasitic relationship. Behavioral Ecology and Sociobiology 41(6):399-406.

Wallin JE. 1992. The symbiotic nest association of yellowfin shiners, Notropis lutipinnis, and bluehead chubs, Nocomis leptocephalus. Environmental Biology of Fishes 33(3):287-292.

 

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About James C. Cureton II

I am a PhD candidate at the University of Oklahoma interested in the ecology and evolution of fishes, most notably Cypriniformes! Check out my personal website (https://sites.google.com/site/jamesccuretonii/) or follow me on Twitter (@Cureton2J) to stay up-to-date with the blog and other information! I am interested in teaching others about this diverse group of fishes and learning about them from others who are more informed! I started this blog to synthesize common and scientific knowledge of this group in a way that will reveal just how spectacular this group of fishes is! I am also interested in learning from others so if you have some useful information, please share it in the comments section!
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