If you have had the privilege to work with different locales of the Oophaga genus, you may have noticed certain locales seem tom produce odd ratios when it comes to the sex of their offspring.
One of the most common questions we hear from keepers is: “Does this locale tend to be male or female heavy?” The honest answer is that sex ratios can vary quite a bit, even within the same species or locality. Some seem to be basically 50/50, as you would expect to see in nature. But for many hobbyists keeping these frogs at home, we have noticed interesting patterns in sex ratios pertaining to certain locales.
Perhaps the most well known example of this would be the Oophaga vicente "Red" locale. At one point, frogger were reporting seeing roughly a 6:1 male to female ratio from offspring, particularly from the "Old/Nahn" line". There has long been debate amongst breeders about what the cause it of this trend. Some have surmised it may be a result of particular temperatures during development. However, science has proven that sex in Oophaga is determined at the moment of fertilization. The same is not true however for phenotypic differentiation, where it can be difficult to know whether the frogs color/pattern is truly genetic, environmental, or a result of other factors. Unlike some reptiles, dart frog sex ratios are not something breeders can reliably control with one simple factor like incubation temperature.
Because of this, young Oophaga are usually sold as unsexed unless they are old enough to show clear signs of sex. Males may start to call around 6 months, show more territorial behavior, or appear smaller and slimmer. Females are often larger-bodied and may become more dominant around feeding or breeding sites, but typically don't start laying eggs until after 12-14 months. Even then, sexing can take time, and some frogs do not show obvious signs until they are more mature, and some males from the same clutch may grow larger than his female counterparts. I've often wondered - Do the parent frogs know the sex of their offspring before they start to mature? Do these Red Vins know just how many males they've been making?!
The interesting part of this topic to me, is the shifts some froggers are starting to notice in certain locales. Using the Red Vin example, I personally started holding back offspring about 18 months ago, in an attempt to try and prove a couple more females for additional breeding pairs. To my surprise, 5 of the next 7 frogs I help back wound up female. The next batch is about 8 months old now, and I only have 1 caller out of 4 subadults. I am no longer experiencing the notorious "ALL MALE" issue, instead I am experiencing essentially the exact opposite. I have made no significant (or even minor) changes to the way I am keeping them, but for some reason am getting much different results. It has really made me curious about what the change is. At this point I can only hypothesize: Do the ratios produced change over the lifespan of the Female? The male? Is there some "magical" Rupert Sheldrake "morphia resonance" going on here? Are the frogs realizing they need to balance things out?
I'm certainly not blaming this phenomenon on magic or fringe scientific theories, but I do find it fascinating. What's causing the ratios to shift for my pair? If it were anything environmental, you'd think I would see the same results from my "Blue Green" vicentei pair, that is houses in an essentially identical tank directly next to the Red Vins. Would most of these sex ratios even themselves out given a long enough timeline? Are there any locales in situ that have this same issue? The laws of nature would seem to say no, but who knows?
As fascinating as I find it, I do find it a bit frustrating that the answers still seem just out of reach. Hopefully there will be more studies done on captive populations, as well as wild populations - so that we can eventually nail down what is responsible for these trends. For now, I am just happy to be producing a lot of female Red Vins to help complete a few of the numerous lonely males or male groups out there!