Sex ratios of snubnose darters
Posted 30 April 2015 - 03:03 PM
The odd thing we've found is that for the four months where sex is easily determined by external observation, January - April, both species have a strong female bias. For those four months, the tennessees have a M/F ratio of 64 to 146, and the blacksides have a ratio of 41 to 88. I don't think I've encountered this in the past; has anyone seen something similar with darters, or have a possible explanation for it? Our collections have been made with a 4 m seine with fine mesh, working up and down a 300 m stretch of the river in riffles and flow pools. I know gear bias is often a factor, but I can't really see it here. Thanks for any thoughts.
Posted 30 April 2015 - 03:20 PM
Posted 07 May 2015 - 09:50 AM
I've noticed a similar trend in snubnose darters (E. barrenense, E. tallapoosae, E. entieri, E. flavum, and several other species) that I've been collecting the past few years. We usually try to get male and females for behavioral analyses and definitely have a harder time getting decent sample sizes for males. I'm not sure why though...
Posted 07 May 2015 - 11:09 AM
Posted 07 May 2015 - 02:42 PM
Sampling bias, perhaps? I've always seemed to land far more female E. barrenense and E. etnieri than males but, other species, like E. pyrrhogaster and E. flavum, have been acquired easily with roughly congruent sex ratios.
Then again, in light of recent phylogenetic work, snubnose has to be used in a broader context. I'm pretty sure that the E. barrenense, E. rafinesquei, and the E. simoterum complex (Ulocentra) is more closely related to E. blennioides types (Neoetheostoma) than to all the rest of the classical snubnoses, such as E. duryi and E. flavum, which are housed in the Adonia clade.
Regardless, all these groups are very closely related, I just always found it puzzling that E. blennioides types (classically part of the subgenus Etheostoma) are wedged between the snubs, which were all traditionally placed in Ulocentra.
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