Pacific Tree Frog: Hyla regilla (Gwen’s notes from David Herlocker Class)
Tree frogs are a whole family of frogs that live in trees. The least arboreal member of the group is our Pacific Tree Frog Awhile back, this frog started being referred to as the Pacific Chorus frog. What was this all about? Tree Frog is in the genus Hyla; Chorus Frog is in the genus Pseudacris. For awhile our Pacific Tree Frog was determined to be more genetically similar to the chorus frogs. So its genus was changed to Pseudacris. Now the pendulum is swinging the other way. This animal has two common names because scientists can’t agree. The frog doesn’t know or care.
Identifying characteristics: Always have dark stripe through eye. So even though we can find many color variations, this is our only frog with a dark stripe through its eye. Enlarged bulbous toes Î allow frog to cling to vertical surfaces. The elasticity of the toe joints and the bulbous toes mean tree frog. (If you find a small red-legged frog – it won’t have toe bulbs.) Color polymorphism: Why are they all different colors? It turns out there are three traits: o Yellow-green o Brown (beige-brown) o Ability to change between yellow-green and brown All frogs can change brightness of their color (temperature, humidity, and stress) due to a hormone that regulates how much melanin is expressed. Almost all of them can get almost black. The environment is never homogenous; ability to change color is not instantaneous.
Vocalization
3 basic calls: Calling starts after first significant fall rain and lasts through June. Diphasic Monophasic Trill Only males sing! (“I wanna woman” “I need a date I need a date” “I’m a guy, I’m a guy”)
Pacific Tree Frog Page 2
Diphasic Krick eck krick eeck If you take a loud speaker to a pond and play the diphasic call … it is a male attractant. It’s a call to gather. The more males that get together and make a call, the more females can hear … they’ll know it’s a good place to come and lay eggs. Females also move toward diphasic call.
Monophasic Reeck / reeck / reeck Signals that a male is on territory and senses movement. He’s saying “Occupied / Occupied / Occupied”)
Trill Held longer (like a monophasic with a trill at the end) This call can mean 2 things 1. Actual contact with another male (“You’re too close to my territory”) 2. Release call (“get off me – I’m a guy”)
Mating happens at night. Courtship happens in the day. At BLP we can hear tree frogs both day and night.
In the frog chorus, we almost always hear 3 voices at the beginning of the chorus: 1. chorus leader (highest pitch) krick eek 2. second (next highest) krick eek 3. third (lowest in pitch) krick eek Then everybody comes in (at first in other triads and then it’s that loud cacophony you hear driving past ponds at night.)
Chorus leader is larger, has a stronger voice, and is in the best spot. If you go to a place where frogs are chorusing and CLAP. The chorus will stop. You can hear the chorus leader and his triad start up, then other triads, then the cacophony. They’ll start up again after about 5 minutes. Next CLAP, two minutes, etc.
Throat pouches of males expand to make sound. When you look at a tree frog, the males will have dark and wrinkly throats.
The Pacific Tree Frog is the frog heard round the world. Hollywood goes out intot he back lot and records. Rent the movie the African Queen and take a listen.
Reproduction Frogs don’t have penises. External fertilization (tailed frogs developed tails because they mate in fast moving water … tail isn’t a penis, it is a way to transfer sperm to female) Female lays eggs and sperm is spilled on top (like salmon) Male rides on back of female; she lays eggs; he releases sperm (Amplexus) Male kind of squeezes eggs out of her Pacific Tree Frog Page 3
Lay eggs in masses (almost as big as the female) Female produces proteins that binds with water and produces mass ,,, kind of like making jell-o Can produce 2 or 3 egg masses per night; 2 or 3 nights per week When just laid, jell-o matrix is completely clear How long do the eggs take to hatch? Variable … early in season when it’s cold, the clear jell-o phase can last 1-3 weeks. Late in season when surface water is warm, the eggs can hatch in the matrix in 4-5 days. So 2 months to 10 days
Eggs Are AMAZING, living breathing things Metabolizing Producing wastes The greenish color that appears in egg mass is actually algae that grow in the jell-o matrix in order to keep the oxygen levels high enough for the eggs!!! (Dissolved oxygen in the egg mass is higher than in surrounding water!!!) Gel also acts as a greenhouse; allows light to penetrate; keeps eggs warmer: Light heats up black eggs and gel matrix keeps heat in Most frogs lay eggs as close to the surface as they can. If you take the egg mass out it droops (egg masses of CA Newts don’t droop – they’re rubberier).
Larval Growth and Development Larva aquatic; tend to be vegetarians; algae is a superabundant food source A tadpole is a vegetarian food processing unit Look at tadpole upside down – can see large coil of vegetarian digestive tract Vegetarians need larger digestive tracts than meat-eaters. There are large numbers of young and a super-abundant food resource; the female frog only has to provide nourishment for a short period. Early in season we see lots of small tadpoles not doing anything. They don’t have mouthparts at first! They lay there for a week or so developing their mouth and living off remnants of their egg nutrition. Pacific Tree Frog Page 4
As tadpoles start developing legs, they are as big mass-wise as they are going to be. There is usually a nice overlap period mid to late spring … which is certainly what we see at the ponds – tadpoles of all sizes and in all phases of development.
Adulthood There is not a single vegetarian adult frog in the world! There are so few things in biology that you can make broad statements about … this is one! What other large group is strictly carnivorous? The frog has to change from being a vegetarian aquatic animal into a terrestrial carnivore! The whole digestive tract needs to change in order to process food. Frogs can’t process food while this change is taking place. That’s what the tail is for! All the muscles in the tail are slowly resorbed and used as food. Froglets need to get away from the crowded environment. They are truly a prey species. They spend their lives not getting eaten by great blue herons and garter snakes. Pacific Tree Frogs can become sexually mature and return in less than a year (marked frogs and observed this). MOST are 2 or 3 year olds. We don’t know how long tree frogs can live. As long as they stay cool and healthy – many years. When they migrate away from the water, they find a crevice or burrow. They feed year- round (at night). The first rains of fall are the cue for frogs to move to the water and the annual pageantry begins! Most of what they eat are invertebrates … mites, spiders, insects. They require movement to catch prey. The distance between their eyes is typically the size of the largest prey they can eat. Frogs don’t have ribs (adaptation for a hopping life style). Lungs inflate bodies (they’re like bouncing balls).