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About Author: Natalie Calatayud

Posts by Natalie Calatayud

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Frog Nanny

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Tending to tadpoles means carefully monitoring water quality and providing a constant supply of food.

Frog nanny is not an official job title, but it’s been my reality this year. I’m the “nanny” for some 1,176 healthy mountain yellow-legged frog (MYLF) tadpoles.  This iconic California species is one of the most endangered frogs in North America. San Diego Zoo Global has been involved in the MYLF recovery program since 2009, and captive breeding has been an important component of our efforts to re-introduce froglets into their natural habitat in the Sierra Mountains. However, with little information on MYLF life history, the care and reproduction of these frogs in captivity presents many challenges.

I have been working on this project full-time since last October. As I enter the lab and look into the 100-gallon containers holding the result of this years’ extremely productive breeding season, a feeling of excitement and nervousness comes over me. It takes about a month and a half for MYLF embryos to hatch out into free-swimming tadpoles, and in the meantime, they require daily preening. Early in the breeding season, I start my day by counting and cataloging over 1,800 embryos. Something like picking ticks off a chimpanzee, this entails cutting through the surrounding egg jelly and extracting any unfertilized or dead embryos from neighboring healthy ones. Sitting at the dissecting microscope, I examine and record what stage of development each embryo has reached every day. By the afternoon, I am all but cross-eyed. I walk around with constant images of beautifully formed black spheres in my mind’s eye. As the embryos grow and thrive, the stress of getting them through the early stage of development is taken over by concerns for stage two of tadpole rearing.

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These black specks are mountain yellow-legged frog embryos.

So what is stage two? We begin by focusing on what tadpoles need. MYLF tadpoles require cold, clean water, constant feeding, and plenty of space to grow. Like most infants, tadpoles are voracious eaters and require a constant supply of food. If too much food is offered, it accumulates in the tank, causing water quality issues. Too little food, and big brother Jake might start nibbling on his smaller sibling Fred. Cannibalism is not uncommon in amphibian species, so all I can do to stop Jake from eating his brothers and sisters is make sure I feed him enough.

Amphibian nutrition is a work in progress, and little is known of individual species’ requirements. This year, I have gone from reproductive physiologist to dietician. Researching amphibian nutrition is complicated by the specific needs of each life stage. Luckily, I have a supporting team of professional nutritionists and a wealth of knowledge and years of experience, courtesy of Brett Baldwin and David Grubaugh, amphibian/reptile keepers at the Zoo.

Controlling water quality is another daily necessity. The difference between clean and pristine can be subtle, and can affect growth and development in ways that may not be apparent until it is too late (like during metamorphosis). Armed with the HACH colorimeter DR-900, a small team of us (Nicole Gardner, senior research associate; Bryan King, research associate; me; and our weekly volunteers, Jaia Kaelberer, Janice Hale, and Jim Marsh) conduct daily screenings of the water in which our tadpoles live. Based on data we have collected on the water quality in MYLF habitat, we have specific parameters to which we can set our water standards in the lab.

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Helping to raise new generations of mountain yellow-legged frogs is challenging, but rewarding.

They say “be careful what you wish for.” This year, we wished for a handful of MYLF egg clutches to be laid and for a couple of hundred embryos to survive. Instead, we got almost 2,000 eggs! As they grow, we become faced with a new challenge—overcrowding. To my relief, the solution becomes clear; together with our partners at the US Geological Survey and the Department of Fish and Wildlife, we decide to split our bountiful cohort of tadpoles into smaller groups. At the end of May, 711 lucky tadpoles made their triumphant way back to the wild, and 400 of their brothers and sisters stayed here with us. They will be “headstarted” and returned to the wild as froglets.

Everyone involved in this project lives and loves every moment. There is nothing more satisfying than watching a life form grow and thrive under your care. This year’s breeding season has exceeded all our expectations. If we take into account that less than one percent of MYLF tadpoles are estimated to survive to metamorphosis and only an estimated 200 adults remain in the wild, everyone currently involved in this project holds the key to this species’ survival. That can be stressful, but it is also a humbling honor. I am happy to speculate that this is going to be a good year for our MYLF program, and that I will have the chance to be part of their journey back to nature.

Natalie Calatayud is a research associate at the San Diego Zoo Institute for Conservation Research. Read her previous blog, Rocky Mountain High: Boreal Toads Going to a Place They’ve Never Been Before.

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Rocky Mountain High: Boreal toads going to a place they’ve never been before

boreal toad

boreal toad

From the window of a fancy trailer, I can see the small town of Alamosa, Colorado, and lying just behind it, the base of the Rocky Mountains. A gateway to all the many outdoor splendors that the Colorado wilderness has to offer, this small town bustles with the comings and goings of natives, as well as passers-through. However, Alamosa hides another interesting little secret. The Native Aquatic Species Restoration Facility, known as NASRF, is part of the Colorado Division of Parks and Wildlife dedicated to the restoration of 10 species of fish native to Colorado. Additionally (and perhaps more importantly for me), NASRF holds one of the largest collections of a single toad species in the US.

The southern Rocky Mountain population (SRMP) of boreal toad (Anaxyrus boreas boreas) is a geographically isolated population of the boreal toad (Anaxyrus boreas). Although the boreal toad is commonly found in the western part of the US, the SRMP is unique due to its limited geographical distribution, which restricts it to high elevations of montane wetland in Colorado, New Mexico, Utah and southeastern Wyoming. As part of a comprehensive plan to restore and manage the SRMP, a specialized group known as the Boreal Toad Recovery Team (BTRT) was established in 1995, and a captive population has been housed at NASRF since 2001. Over 600 individual toads from different localities in the wild are held and bred as a genetic assurance colony, from which tadpoles are re-introduced annually.

Alaomosa

Alaomosa, Colorado

Amphibians are a curious group of animals. The diversity of physiological adaptations and environmental requirements makes breeding them in captivity difficult. Such is the case with the Boreal toads at NASRF.

One of the most interesting adaptations of the boreal toad is its ability to hibernate. Because they are found at high altitudes and latitudes, they have evolved this behavior to cope with long, harsh winters. However, hibernation in amphibians is not exactly the same as in mammals. In fact, the proper term for this behavior in amphibians is brumation. Like hibernating mammals, temperate amphibians lower their metabolic rates in response to falling temperatures in fall and winter. They stop eating and reduce their activity, but unlike mammals, they do not become dormant. At the beginning of spring, as temperatures rise, boreal toads come out of hibernation and immediately begin to breed.

Although temperature appears to be a key factor influencing reproduction in the Boreal toad, we are not sure how other important factors such as light and nutrition affect adult health and reproduction. At NASRF, we provide special UV lighting to emulate natural day and night cycles, a diverse diet, controlled water temperature, and artificial hibernation during the winter months. In short, we do what we can to replicate the outdoors, indoors.

Sancho

Sancho

In May of 2014, I made the long 1,000-mile drive from San Diego to Alamosa to join the staff at NASRF, in preparation for boreal toad breeding season. That’s not me in the photograph, that’s my trusty partner, Sancho. Seventeen hours later, we arrived at our new and very swanky home, where we would reside for the next 4.5 months. Now I guess I should explain why I told you all about the boreal toad in the beginning, and more importantly, where I fit into the picture. As I mentioned, during the winter months, boreal toads hibernate in the wild. To emulate this at NASRF we use giant refrigerators (the kind you find in restaurants). We box the little toads up with soft, moist sand and peat moss, and put them to bed for five to six months. Odd as this may seem, this period of cold is exactly what these toads need to get them in the mood for love and romance. Emerging from hibernation is like traveling to a sunny beach destination with your partner for a romantic holiday after surviving a long winter.

So, where do I come in? I am a reproductive physiologist working for the San Diego Zoo’s Institute for Conservation Research. About four years ago, I moved to the US to work on amphibians as a post-doctoral fellow at the University of Mississippi. During my post-doc, I concentrated on the application of assisted reproductive technologies to promote reproduction in captive amphibians. When natural matings occur in boreal toads we expect to see certain reproductive behaviors, such as males amplexing females. This clasping behavior may persist for days while the male stimulates the female to deposit her eggs. When breeding does not occur or a female fails to release eggs naturally, I inject females with hormone treatments designed to elicit egg deposition. I also use the same hormones to induce sperm production in males.

Boreals amplexing

Boreals amplexing

Like in humans, ultrasound helps us monitor female toad reproductive cycles by visualizing the ovary and determining the presence and size of eggs. This helps us know if a female that has not bred is ready to deposit eggs. If so, I would inject her with hormones. Once eggs have been deposited, we count the number of eggs that have been fertilized and are cleaving (dividing). Embryonic development is recorded by looking at embryos every day and cataloging different developmental stages.

We raise tadpoles in captivity until they reach a certain size and have developed back legs, before transporting them to the Rocky Mountain National Park for release into the wild. This final stage of the adventure is managed and monitored by the dedicated staff at NASRF and the National Park. Saving the SRMP boreal toad is a collaborative project, with the ultimate goal of restoring these animals in their natural habitat.

(I’d like to thank all the staff at the Native Aquatic Species Restoration Facility for their help).

Natalie Calatayud is a research associate at the San Diego Zoo Institute for Conservation Research.