Friday, May 19, 2017
Tuesday, May 16, 2017
Friday, May 12, 2017
I know what you’re thinking: “Why hasn’t she written about cuttlefish mating systems?” I understand, cuttlefish are ridiculously cool and you just need to know more about them. You are in luck as a brand new study has been published online about just that topic!
Cuttlefish are cephalopods, which are all predatory, marine animals that have at least eight arms, a siphon for jet-propulsion, and highly developed nervous and sensory systems (specifically the most sophisticated eye of all invertebrates). Those last characteristics make them highly intelligent, with complex learning behavior, to the point that many consider them to be “conscious.” Unlike other cephalopods, all of their hard parts (if any) are internal. That means all of their outside parts are soft, squishy and covered in color-changing skin. Their ability to change color is absolutely amazing, particularly in cuttlefish (just google ‘Flamboyant Cuttlefish’!). Located in their skin are tons of chromatophores (pigment filled bags) that expand or contract to reveal/hide their color. And it’s crazy-fast too. They can alter their appearance in as little as half a second! They use this color change for camouflage, courtship rituals, or just to show you how they feel about you interrupting them with your dive camera (a little personal experience with a mama octopus thrown in there).
Cuttlefish are in the clade Coloidea that also includes squid and octopuses, and a sister group to the Nautilus. They look like squid but have stouter bodies and a fin fringe that runs around their body that they undulate to move. They have separate sexes and an often elaborate courtship ritual. Should a female find a male worthy, she accepts his spermatophore (sperm packet), which he transfers to her with a specially modified arm (hectocotylus). Then the females will use the contents of this packet to fertilize their eggs and lay them in clusters.
Cuttlefish can be seasonal in their mating habits, with some species gathering in the hundreds to find their special someone. Where animals gather to mate, they also gather to strut their stuff. One of the ways they do this is through shear brawn. Basically, the strongest guy gets the girl. A study currently in press in The American Naturalist describes competition between male cuttlefish. Males compete vigorously for female mates. The researchers took a close look at the Common Cuttlefish (Sepia officinalis), a species “renowned for its visual capabilities, rapid adaptive camouflage, learning, and memory.” All those amazing qualities and yet oddly lacking in its ability to identify individual mates or rivals. Seriously, telling boy from girl is a challenge. This means that they must use a signal-response system to recognize each other. This system employs the use of intense zebra-stripe displays. Respond to a zebra with a zebra and you are male. If you don’t want to fight, darken your whole body (sign of alarm), ink and jet away. But extend your fourth arm, darken the skin around your eyes, and dilate your pupils and you know that shit is about to get real: inking, swiping, grappling, lunging, rolling, and biting. An all-out cuttlefish brawl.
A lot of this information is known from lab studies of cuttlefish, but how do they act in their natural environment. To test this, the researchers went to the Aegean Sea near Çeşmealtı, Turkey and filmed a bunch of cuttlefish. They brought the footage back to the lab to analyze mate guarding and fighting behaviors, frequencies of a series of agnoistic behaviors in individual males, and aggressive behaviors (e.g., bar room brawl scenario). Since it all starts with the zebra stripes, they also compared the intensity between males. They found a generalized sequence of events that correlated to the amount of aggression. For example, just a dark ring around the eye is low-level aggression, adding a dilated pupil ramps it up to medium-level aggression, intensifying the zebra pattern and arching and tilting the body ramps it up even more. The more medium- to high-level aggressive behaviors the more likely the male was to win. The researchers summarize it this way: “weak zebra banding, fourth arm extension, dark eye ring > dark eye ring with dilated pupil, dark face, strong zebra banding, inking > intense zebra display > swiping, grappling > biting, rolling.” This makes sense if you think about it. Fighting may result in injury and injury is costly, sometimes fatal. So you need to make sure you can win. The series of stages allow each male to assess both themselves and their opponent to see if an actual brawl is worth it.
Now, take what you’ve just learned and apply it to this video. It shows exactly the type of bout the authors describe. You may need to watch it twice, once to read the descriptions of what is going on and another to watch for the subtle differences described above. Can you see the color and eye changes?
Just imagine what we will find out as camera systems get faster. Considering the extremely fast rate at which cuttlefish are able to change their colors, it is very likely that we are missing a lot of the more subtle details in communications between males (and probably with females too). We’ll have to revisit this subject in the future.
Allen, J., Akkaynak, D., Schnell, A., & Hanlon, R. (2017). Dramatic Fighting by Male Cuttlefish for a Female Mate The American Naturalist DOI: 10.1086/692009
Learn more about Cephalopods at the University of California Berkeley’s Museum of Palentology and the Monterey Bay Aquarium
Image from the Monterey Bay Aquarium
Posted by Melissa Chernick at 5/12/2017
Thursday, May 11, 2017
Tuesday, May 9, 2017
Wednesday, May 3, 2017
|Ubatuba, São Paulo, Brazil; 9 October 2014 © Almir Cândido de Almeida|
First, a little background on hummingbirds. They belong to the family Trochilidae and are closely related to swifts. Males are typically more colorful that females, having highly reflective feathers on their chest and heads. Perhaps these birds are best known for their unique flying. They are able to produce power with both the down- and up-beat of their wing flap, getting 75 percent of their lift from their wings’ downstroke and the remaining 25 percent from the upstroke. This allows for both increased agility and sustained hovering ability. They are the only birds that truly hover and fly backwards. They also move those wings really fast: 60 times per second! So it is little wonder that they have among the highest metabolic rate among vertebrate animals.
Hummingbirds are specialized and consume predominately nectar. To collect enough nectar to maintain that high metabolism, they forage many flowers each day. But not all flowers are created equally. Their sugar concentration can vary between 20-25 percent. In order to get the most sugar-bang for their hover-buck, hummingbirds must select and protect the richest food patches in their area. Three behavioral strategies have been observed for foraging:
1) Dominance/territoriality – a bird will defend its flowers
2) Intruder/subordinance – a bird sneaks into other patches until it is kicked out
3) Trapline foraging – repeatedly visiting a set of plants in different patches without being territorial.
Often, a bird will perch near a good food source and let others know that it is theirs. But defending a territory can be up to three times more energetically expensive, so those flowers need to be really good.
The researchers conducted their study in Itacolomi State Park in the city of Ouro Preto, Minas Gerais, southwestern Brazil, in the Atlantic forest remnant. They created four artificial food patches, each patch containing a single sugar-water solution concentration of 5, 15, 25, or 35 percent. They observed the birds (using binoculars) for 3 hour stretches in the early mornings and late afternoon, recording all behaviors during that time. They looked at the time spent in each food patch and the behaviors of the birds (feeding, alert, vocalizing, expelling, fighting, frightening, expel attempt) in each patch. In this way, they could identify the birds’ strategies.
They found that the most-visited feeders were those containing the highest concentration of sugar. Five of the seven species observed fed more on the 25-35 percent sucrose feeders. But there was a difference in the frequency of visitations for different species. The Brazilian ruby (Clytolaema rubricauda, pictured above), Scale-throated hermit (Phaethornis eurynome), and Phaethornis spp. visited the 35 percent feeder more often. And the Brazilian ruby won most of the aggressive encounters with other hummingbirds, both total and in individual patches. This species often stood alert and fought more often, and even “stood impassive” when faced down by the Violet-capped woodnymph (Thalurania glaucopis). I wonder if they looked down their long little beaks at the other birds with a f*ck off attitude? What a badass...hmm, or a bully. The Violet-capped woodnymph visited the 25 percent patch more often, the White-throated hummingbird (Leucochloris albicollis) and Versicoloured emerald (Amazilia versicolor) visited the 15 percent patch more often, and the Glittering-bellied emerald (Chlorostilbon lucidus) was the one that less frequently visited the food patches. Interestingly, the Phaetornithinae applied a hide-and-wait strategy, where they would be chased away by the territorial bird only to hide in the shrubs, remain quiet, and return to the feeder after the dominant bird left the area. Sneaky sneaky. The time spent feeding was found to be correlated with aggressive behaviors and also with body size. Big birds, big appetites, big aggression. The subordinate species chose resources depending on the presence or absence of the dominant species, preferring patches that were not guarded. This may be why they were seen in lower concentration sugar patches more often.
Those itty bitty birds can pack some serious aggression. I guess it isn’t really surprising after seeing all of the chasing that goes on around my feeder. Yackety Sax remains appropriate.
Lanna, L., de Azevedo, C., Claudino, R., Oliveira, R., & Antonini, Y. (2017). Feeding behavior by hummingbirds (Aves: Trochilidae) in artificial food patches in an Atlantic Forest remnant in southeastern Brazil Zoologia, 34, 1-9 DOI: 10.3897/zoologia.34.e13228
If you would like to put out your own hummingbird feeder, I recommend this kind because it is simple, inexpensive and does a great job.
The important part is the big red flowers with yellow centers. Hummingbirds really hone in on those color ques. Do NOT use honey in your feeder! And forget the red dye, if your feeder has red color on it then that is plenty to attract the hummingbirds.
Here is a nice and simple recipe to make your own hummingbird food:
¼ cup granulated sugar
2 cups water
Mix the ingredients in a small saucepan. Bring to a boil. Boil for a few minutes or until all of the sugar is dissolved. Let cool to room temperature. Whatever doesn’t fit in the feeder can be stored in the refrigerator.
Increase the recipe as needed, it's a 1:4 ratio of sugar:water
Change the solution in the feeder every 3 days, sooner if it is really hot outside. Make sure to rinse the feeder each time it is refilled. Scrub away any growths (fungi, etc.) as needed.
Brazilian Ruby picture via The Cornell Lab of Ornithology
Feeder image via World of Hummingbirds