Welcome to the Part III of “my first blog post!” Part I provided insight into what a Cypriniform is and the distribution of species )across families. Part II focused more on what these fish look like and the final episode of my first post, Part III, will focus on the evolutionary history of this group (or at least what we know to this point)! Before we jump into the evolutionary history of this group, it is worth briefly this question: What is a phylogeny? A phylogeny is a hypothesis of evolutionary relationships among some organismal groups of interest (e.g., populations, species, families, etc.). It essentially assess how these groups are related based on some aspects of the genome, morphology, physiology, behavior, or any other trait that can be qualified/quantified. Depending on the type of data (e.g., genomic vs. morphology), different techniques and algorithms (e.g., parsimony, likelihood, Bayesian) can be used to build the hypotheses. One important point to remember is that a phylogeny is only a hypothesis. It can change with the addition of new evidence. If the concept of a phylogeny still isn’t clear, check out this site from Berkley or just google “what is a phylogeny.” Plenty of web sites will emerge. It’s probably best to first take a look at the broader evolutionary history of Cypriniforms (e.g., what are they closely related to? how long ago did they diverge?) before talking about loaches, suckers, and minnows! So, how did Cypriniforms come to be? Cypriniforms are part of a well-defined group known as Ostariophysi, a group that includes Gonorynchiforms (milkfish, et al.), Cypriniforms (loaches, minnows, and suckers), Gymnotiforms (South American knifefish), Characiforms (characins), and Siluriforms (catfishes) (look here; Betancur-R et al. 2013). Using a series of fossil calibrations and analytical techniques, Betancur-R et al. (2013) estimated the Cypriniforms to have last shared a common ancestor with all other Ostariophsyi at about 170 +/- 25 million years ago (MYA). This basically means that the lineage of little fish we classify as Cypriniforms showed up on earth around 170 MYA. Let that sink in… … 170 MILLION years ago. Do you know what was roaming the earth then that isn’t alive today? Dinosaurs. Yep, these bad ass little fish survived whatever catastrophes wiped out teeth gnashing Tyrannosaurus and ginormous Argentinosaurus, a 30+ meter, 80+ tonne dinosaur. That’s pretty spectacular, right??!?! Agreed!! With regard to Cypriniforms, the other inference we can draw from this paper is that minnows (Cyprinoidei) diverged from loaches and suckers (Cobitoidei) around 100 +/- 30 MYA. So, before dinosaurs ever went extinct, there were two lineages of Cypriniforms, one that ultimately led to loaches and suckers and one that led to minnows. One interesting question that hasn’t been answered yet: what caused the split of the minnow lineage with the lineage that led to loaches and suckers? Good question and honestly, I haven’t seen a good answer although I will venture to take a guess. If you read my last post, I mentioned that loaches are uniquely adapted to high flow habitats – they have (generally) flat ventral bases for adhering to the substrate, smooth streamlined dorsal sides, and large paired fins attached on a horizontal plane – whereas minnows are (generally) more adapted to living off the substrate – they have laterally compressed bodies and paired appendages on a more vertical (or diagonal) plane. So, one might hypothesize that suckers and loaches evolved to live on the substrate (termed benthic fish) whereas minnows adapted to life in the water column (termed pelagic fish). Specifically, adaptation to each environment drove reproductive isolation and ultimately led to speciation. Now, obviously this isn’t adequate to explain all the diversity in this group, but it is a starting hypothesis that needs more data to be thoroughly accepted or rejected. OK, so let’s take a more in-depth look at evolutionary relationships within each of the two suborders. The most thorough look at morphology in loaches was published in 1982 (Sawada 1982). If you are interested in loaches, you should give it a read. Mayden et al. (2009) also provided insight into phylogenetic relationships of Cobitoidei using four (out of thousands) nuclear genes and thirteen (out of thirteen) mitochondrial genes. Generally, they recover relationships as shown in the picture with a few exceptions: Mayden et al. (2009) didn’t sample Serpenticobiditidae or Ellopostomatidae, but they did sample Botiidae (recognized as a subfamily of Cobitidae in the Catalog of Fishes); the locations of Balitoridae and Nemacheilidae are switched.
After posting this blog, one of my colleagues pointed out a paper I glaringly missed (thanks Milton!) which is perhaps the most thorough attempt at resolving major relationships among the lineages of Cypriniforms (Mayden and Chen 2010).
The authors used six nuclear genes and with regard to loaches, largely found the same results among the sampled families as Mayden et al. (2009). Although not included in this phylogenetic hypothesis, the authors previously suggested Ellopostomatidae was sister to Nemacheilidae (Chen et al. 2009). As far as I know, Serpenticobitidae and Gastromyzontidae haven’t given a phylogenetic treatment (yet). Nonetheless, studies like Sawada (1982), Mayden et al. (2009), and Mayden and Chen (2010) (among others I haven’t referenced here for time sake) have laid the foundation of our understanding of how suckers and loaches diversified — shown in the figure above –over the last 100 million years . What about Cyprinoidei? Well, that’s a whole ‘nother story. As I mentioned earlier, there are at least 2,960 species in this suborder and at least 14 subfamilies. At least. Given that we don’t have a good idea of the diversity and how it all will be taxonomically filed, it’s impossible to come up with a good phylogenetic hypothesis to explain this diversity. One (potential) attempt to explain evolutionary relationships among most of the subfamilies was based on skeletal characteristics and seems like it could be an excellent starting point (Xiang-Lin et al. 1984). Other attempts to resolve the relationships have been made based on single genes (He et al. 2008). As with Cobitoidei, the most thorough treatment of Cyprinoidei may be by Mayden and Chen (2010). These authors sampled 14 subfamilies of Cyprinoidei and recovered relatively strong support for their relationships (again, based on six nuclear genes).
The recovered relationships are shown above with me using subfamily names (rather than the elevated family names as they used in the paper). The support for most of these groups is relatively high although additional subfamilies still need to be sampled. One particularly interesting findings it that Psilorynchidae is sister to Cyprininae. This is interesting because it would seem to suggest that Psilorynchidae (a taxonomic rank of family) should be demoted to Psilorynchinae subfamily) in order to keep Cyprinidae monophyletic. Realistically, Cyprinidae and Psilorynchidae will probably remain as families although Cyprinidae likely will be broken into multiple families (e.g., as suggested in Mayden and Chen 2010). Only time and more data will tell! Nonetheless, this paper provides an excellent starting point for additional work on this group. It’s worth noting that relationships within even some of the subfamilies have been difficult to resolve. For example, the Notropis radiation within the subfamily Leuciscinae has proven excessively difficult to resolve. Some subgenera (Notropis species classified into smaller taxonomic groups) have been delineated (e.g., Hydrophlox; Cashner et al. 2011), but relationships among Notropis are largely unresolved. So why do phylogenetic relationships matter? Because our goal is to understand and explain the patterns that generated the amazing diversity around us. Without phylogenetic relationships, it is next to impossible to do. In other words, without a good understanding of the evolutionary relationships of Cypriniforms, we can’t understand why there are so many little bad ass minnows that survived catastrophes even the dinosaurs couldn’t!
Betancur-R R, RE Broughton, EO Wiley, K Carpenter, JA Lopez, C Li, NI Holcroft, D Arcila, M Sanciangco, JC Cureton II, F Zhang, T Buser, MA Campbell, JA Ballesteros, A Roa-Varon, S WIllis, WC Borden, T Rowley, PC Reneau, DJ Hough, G Lu, T Grande, G Arratia, G Orti. 2013. The tree of life and a new classification of bony fishes. PLOS Currents Tree of Life, doi: 10.1371/currents.tol.53ba26640df0ccaee75bb165c8c26288.
Cashner MF, Piller KR, Bart HL. 2011. Phylogenetic relationships of the North American subgenus Hydrophlox. Molecular Phylogenetics and Evolution 59:725-735.
Chen WJ, Lheknim V, and Mayden RL. 2009. Molecular phylogeny of the Cobitoidea (Teleostei: Cypriniformes) revisited: position of enigmatic loach Ellopostoma resolved with six nuclear genes. Journal of Fish Biology 75(9):2197-2208.
He S, Mayden RL, Wang X, Wang W, Tang KL, Chen W-J, Chen Y. 2008. Molecular phylogenetics of the family Cyprinidae (Actinopterygii: Cypriniformes) as evidenced by sequence variation in the first intron of S7 ribosomal protein-coding gene: Further evidence from a nuclear gene of the systematic chaos in the family. Molecular Phylogenetics and Evolution 46:818-829.
Mayden RL, WJ Chen, HL Bart, MH Doosey, AM Simons, KL Tang, RM Wood, MK Agnew, L Yang, MV Hirt, MD Clements, K Saitoh, T Sado, M Miya, and M Nishida. 2009. Reconstructing the phylogenetic relationships of the earth’s most diverse clade of freshwater fishes-order Cypriniformes (Actinopterygii: Ostariophysi): a case study using multiple nuclear loci and the mitochondrial genome. Molecular Phylogenetics and Evolution 51:500-514
Mayden RL, Chen WJ. 2010. The world’s smallest vertebrate species of the genus Paedocypris: a new family of freshwater fishes and the sister group to the world’s most diverse clade of freshwater fishes (Teleostei: Cypriniformes). Molecular Phylogenetics and Evolution 57:152-175.
Sawada, Y. 1982. Phylogeny and zoogeography of the superfamily Cobitoidea (Cyprinoidei; Cypriniformes). Memoirs of the Faculty of Fisheries Hokkadio University 28(2):65-223.
Xiang-Lin C, Pei-Qi Y, Een-Duan L. 1984. Major groups within the family Cyprinidae and their phylogenetic relationships. Acta Zoological Sinica 1984(4): ??