Toads, sticklebacks, and aphids…

A short visit to Gustavus in mid-July yielded a diversity of interesting observations. My friend had a report of toads near a gravel pit, so we went out to see. We found the place teeming with human kids and parents, actively (and loudly) enjoying a swim on a very hot day (over eighty degrees; that’s sweltering in Southeast!). So we dove into the woods instead, wandering here and there, and on our way back to the car, we noticed some very odd tracks in the dusty road: Toes of uneven length, the stride a sweeping motion through the dust. Can’t be a mammal or a bird—aha, it was a toad, walking (with toes dragging) instead of hopping for many yards in the roadway. Very cool—I’d not seen such clear toad tracks before this.

Late that evening, we returned to the pond, when the human crowd had gone home. Now we could see dozens of tiny toadlets hopping about in the brush that fringed the pond. In the shallow water there were tadpoles at various stages of transformation into toadlets: some fat-bodied tadpoles with no hind legs worth mentioning and a stout tail, some almost-transformed toadlets with little tail left and good swimming legs, and others in between.

Seeing all these stages of development prompted me to wonder about how a developing toad changes its diet. Tadpoles are considered to be herbivorous, in general (although some species are carnivores), grazing on small particles in the biofilm of algae, bacteria, and perhaps fungi that grows on the surface of rocks and weeds or filter-feeding on planktonic algae. Toadlets and adult toads forage on insects, capturing them with a long tongue and swallowing them whole. Changing from vegetarian to meat-eating necessitates major changes in the feeding apparatus and digestive tract. The small tadpole mouth disappears, replaced by a wide mouth, a jaw, and a tongue. The stomach gets bigger. The intestine becomes shorter and better supplied with absorptive surfaces. New enzymes are produced. During the principal time of change, the animal actually stops feeding until the changeover is complete. That might explain why just-emerged toadlets often look so thin. Then the newly equipped toadlets have to learn how to forage effectively for bugs. That seems like a big job!

Swimming with the tadpoles were lots of sticklebacks. There were schools of tiny hatchlings and plenty of fat, gravid females with a load of eggs inside. They will seek out a nest made by a male and lay their eggs inside, for him to tend. A male fans a nest with his pectoral fins to improve water and oxygen flow and defends it against potential enemies. Nests are small tunnels built of bits of debris and algae, and they are hard to find. However, Bob Armstrong has a nice video of a male guarding and fanning his nest (search for this at naturebob.com).

The next day we took a walk through the grassy, sedge-y meadows that stretch from the forest to the beach. Near the start of the trail we saw several families of barn swallows, all lined up on a wire or packed into a shady corner, still being tended by busy parents. There were Lincoln’s sparrows at the edges of willow clumps and alder flycatchers singing in the thickets.

One of our goals was finding some sweetgrass (the common species that grows here apparently goes by two scientific names, depending on which book you consult: Hierochloe odorata or Anthoxanthum hirtum). Sweetgrass has been used by native cultures around the northern hemisphere for its aroma and for braiding into basketry. We found it easily, its quite distinctive inflorescence mixed in a community of other species. Of course, we gathered a little and made a couple of simple braids, just for fun; for practical use, the stems should be gathered earlier in the season when they are greener and more pliable.

Canada goldenrod was flowering splendidly, and a number of plants had infestations of aphids. Some of the aphids had wings. We were amused to see that when these wee insects were approached by a finger, they tended to rear up their hindquarters, often in a wave proceeding up the stem, a bit like The Wave performed by sports-fans in an arena. Other kinds of aphids do something similar. For the aphids, this could be some kind of defensive reaction, but against whom?

There was other good stuff to be seen and heard. At the edge of the forest, we looked at two empty chickadee nests, one in an old snag and one in a nest-box. To our surprise, both nests were simple thick mats of moss, without the expected cup in which eggs and chicks would nestle. We were entertained by juvenile nuthatches calling continuously from the conifers in hopes of parental attention. We visited the site where a winter-killed moose carcass had attracted scavengers, including coyote and marten (as recorded earlier on a trailcam). By now, nothing was left but scattered bones, hooves, and hair. This beast had been an old fellow, with badly worn teeth, although his stomach had had some food in it. Out on the bare sand flats, we saw some prodigious brown bear tracks, accompanied by those perhaps of a two-year old.

A good visit in excellent company!

Parental care by males

Some months ago I was captivated by a grunt sculpin at the NOAA lab, and I learned that males of this species commonly guard their mate’s eggs. When it is time for the eggs to hatch, the parent takes up the eggs in his mouth and spits them out into the water column, where the egg membrane breaks and the hatchlings are freed. Then I saw a video of a male three-spined stickleback guarding his nest from all comers (see naturebob.com); the accompanying photo is taken from that video. And all that prompted me to think more about paternal care, particularly among vertebrates. In some species either parent or both parents may be involved with parental care, but here I am concerned chiefly with vertebrate species in which males are the sole caregivers (it happens among the invertebrates too, but that’s another story). Strictly paternal care is generally less common than strictly maternal care, except in fishes, among which fatherly care is more common.

The more I thought about it, and the more I read on the subject, the more it seemed necessary to divide the intended essay into two parts, so as to cover some of the fascinating variation that is found concerning how males care for their young. In general, solo-male parental care among fishes is considered to be best developed in freshwater and small-bodied species; among both fishes and amphibians, it is most common in species with external fertilization of the eggs. Although the evolution of fatherly care has been much discussed and is still debated, here are some of the exotic parental things that male fishes and amphibians do.

The fishes offer the most fantastic array of different ways to take care of eggs and babies. The males of several very different, unrelated species customarily build nests; here are just a few examples. A male stickleback (the three-spined Gasterosteus, the nine-spined Spinachia) builds a nest and invites females to lay their eggs there. He then guards the nest against other males and potential predators, also fanning the eggs with his fins to provide a good flow of oxygen. Males of freshwater sunfish (Lepomis) scoop out shallow nests in the bottoms of lakes and ponds. They invite females to lay eggs and defend the eggs until they hatch. Again, one male may have eggs of several females in his nest (and females may mate with more than one male, too). Stream-dwelling johnny darters deposit eggs on the undersides of flat rocks. Males defend those clutches of eggs, and they also maintain sanitary conditions by removing any eggs that get infected by fungi. A male Siamese fighting fish (Betta splendens) makes a bubble nest, retrieving any eggs or hatchlings that fall out and repairing the nest as needed.

Males of sea horses (Hippocampus) take things one step farther: females deposit their eggs in a pouch on the male’s belly, where fertilization occurs. The males incubate the eggs and brood the hatchlings in that pouch—a sort of movable nest. The male’s pouch provides not only a controlled environment, but also oxygen, hormones, calcium, and lipids full of energy (in addition to the yolk of the egg), and waste management. Although apparently each brood of eggs is provided by one female, when one brood matures and leaves the pouch, the male can then mate with another female. In the related pipefishes and sea dragons, males carry the eggs either in a pouch, like the sea horses, or under his long tail.

The males of at least one species of Kurtus, a fish of slow-moving fresh and brackish waters, carry clumps of eggs on a vascularized hook on the forehead. Apparently it is still unknown if the blood supply serves to deliver nutrients to the eggs. Still other fishes brood eggs and hatchlings in the mouth of the male parents (some tilapias, a sea catfish Ariopsis, and a particular species of Betta). How offspring are distinguished from prey—an important distinction!—is unclear.

Possibly less complicated is the behavior of a tropical fish sometimes called the splash tetra (Copeina arnoldi). Male and female leap together out of the water and spawn, very quickly, on an overhanging leaf, before dropping back into the water. The male then spends a few days splashing the eggs to keep them wet and oxygenated until they hatch, and the hatchlings fall into the water.

Among the amphibians, both biparental and uniparental care occur; solo-male parental care is known from several species. For example, in the giant salamander known as the hellbender (Cryptobranchus), the male excavates a shallow scoop in the mud, where he fertilizes the eggs of each female that chooses to use his nest. He then tends the accumulated eggs (those that survive cannibalism), moving about the nest to circulate the water and keep up the oxygen supplies for the eggs. His incubation time lasts for several weeks, sometimes months.

Some male frogs build small mating pools in which eggs are laid. Males of other species carry eggs on their bodies. In one of the tropical poison-dart frogs (Phyllobates bicolor), the males tote their tadpoles on their backs, carrying them from puddle to puddle (related frogs apparently have biparental care). Male European midwife toads (Alytes obstetricans) carry a bunch of eggs on their rear ends.

Males of Darwin’s frog (Rhinoderma darwinii) in southern South America are dedicated parents. Each male guards a clutch of eggs for many days. When they are nearly ready to hatch, he takes them up with his tongue and stuffs them into his vocal sacs, which extend down his back and belly. There they hatch and grow, living off their yolk and secretions from the vocal sacs, until they metamorphose into froglets and hop out of their father’s mouth. That would be a sight to behold!