DNA barcoding reveals Astroblepus diversity

[Silurus]

Hernández-Zapata, M, LE Ochoa-Orrego & LF Jiménez-Segura, 2018. Métodos de ADN Barcode revelan diversidad de especies de Astroblepus en la cuenca del río Porce, Colombia [DNA Barcode methods reveal diversity of Astroblepus species in the Porce River drainage, Colombia]. Actualidades Biológicas 40: 59–71.


Resumen
El género Astroblepus es endémico de la región Andina y está representado por aproximadamente 81 especies válidas que habitan ríos de alta montaña desde Panamá hasta Bolivia. Para Colombia, se han registrado 32 especies, de las cuales 23 fueron registradas en monitoreos recientes en la cuenca del río Porce, indicando que cerca del 71% de la diversidad de especies se encuentra en esta área. Morfológicamente, las especies de Astroblepus son muy similares y los caracteres empleados tradicionalmente para su determinación son poco resolutivos, lo que dificulta su identificación taxonómica. Con el objetivo de determinar la diversidad de Astroblepus en la cuenca del río Porce, se analizaron 129 individuos empleando herramientas de identificación genética mediante la secuenciación del gen Citrocromo Oxidasa sub-unidad I (COI) de 580pb y un análisis morfométrico basado en proporciones corporales, usando 12 hitos morfológicos. Los análisis genéticos y el método de delimitación de especies “General mixed Yule-coalescent”, indicaron la presencia de 12 entidades taxonómicas, las cuales fueron soportadas por sus distancias genéticas y por 13 medidas corporales basadas en proporciones. Los resultados indican que la diversidad de especies en el área ha sido sobreestimada, por lo que es necesario integrar diferentes metodologías para una correcta delimitación de especies.

Abstract
The genus Astroblepus, is endemic to the Andean region and is represented by 81 valid species inhabiting high mountain rivers from Panama to Bolivia. In Colombia, about 32 species of this genus have been reported, of which 23 were recorded in the Porce River drainage, which indicates that about 71% of species diversity can be found in this area. Morphologically the species of Astroblepus are very similar and the characters traditionally used for their determination are not very diagnostic, which limits their identification at species level. In order to determine the diversity of Astroblepus in the Porce River drainage, 129 individuals were analyzed using genetic identification tools through the sequencing of the 580bp Cytochrome Oxidase subunit I (COI) gene and an analysis based on morphometry. The genetic analyses and the method of delimitation of species "General mixed Yule-coalescent", indicated the presence of 12 taxonomic entities, which were supported by genetic distances and by 13 body measurements based on corporal proportions. The results indicate that the diversity of species has been overestimated in this river and highlight the importance to integrate different methodologies in the delimitation species studies.

[Bas Pels]

If one collets 129 individuals, expecting them to be devided over 23 species, one would expect 5 of each species.

Still, in all reality there are always some species much more abundant then others. Now I know nothing about Astroblepus, but most likely it will have a pattern much like other genera - a few dominant species and a lot more specialized ones. Found only in darkness or something.

Therefore, if one would collect only 129 individuals, one would expect a few species to be missing.

I think, if one would be able to put the above into statistics, the sudie would be quite less impressing then is feels - basically it says only half the expected species were found.

[panaque]

If one collets 129 individuals, expecting them to be devided over 23 species, one would expect 5 of each species.

Still, in all reality there are always some species much more abundant then others. Now I know nothing about Astroblepus, but most likely it will have a pattern much like other genera - a few dominant species and a lot more specialized ones. Found only in darkness or something.

Therefore, if one would collect only 129 individuals, one would expect a few species to be missing.

I think, if one would be able to put the above into statistics, the sudie would be quite less impressing then is feels - basically it says only half the expected species were found.

You are right of course. I pulled the number of individuals of each 'species' from the paper to produce this rarefaction curve:

astroplot.jpeg (17.77 KiB) Viewed 1085 times

What this shows is the number of species you would expect to find (y-axis) if you randomly pull a given number of specimens (x-axis) from the sample. If you have (more or less) sampled all species in your site then the curve should be levelling off at your total sample size (129 in this case), which it clearly doesn't.

There are various methods for extrapolating from this data to estimate the true species richness (the asymptote of the curve). The most conservative method gives 20 +/- 8. So the data do not support the conclusion that Astroblepus diversity in the Porce river has been overestimated.

[Bas Pels]

Wow, you must know a lot of statistics

I think the curve was drawn assuming an even mixture of the species? That is, chances of being taking in the sample are for each species similar.

Most likely, this will not be the case, increasing the value of 20 +/- 8 even higher.

[panaque]

Wow, you must know a lot of statistics

I think the curve was drawn assuming an even mixture of the species? That is, chances of being taking in the sample are for each species similar.

Most likely, this will not be the case, increasing the value of 20 +/- 8 even higher.

Occupational hazard
No such assumption. The curve is based on the relative abundances of all species in the sample of 129. Some are represented by dozens of specimens others by a single one.