Polyandry is rare because in most cases natural selection has favored for females to be choosy and seek the best possible breeding opportunities because they have a greater parental investment and few expensive gametes, while males have many cheap gametes and are limited by access to females so they would achieve greater reproductive success if they reproduce with multiple females.
You are here
Extreme sexual displays and ornaments are found in species with promiscuous mating because they are subjected to strong sexual selection. This strong sexual selection is due to lots of variability in reproductive success, with a few males monopolizing reproduction, and a high cost for breeding successfully. (According to Bateman’s gradient, the steeper the slope the stronger the sexual selection).
This species is adapted for diving and swimming in water thanks to its modified rear limbs. The bones of the feet are longer than usual and can extend like a fan under water, in a similar way as its hind limbs have modified fingers that give the shape of the wings. These extended membranes are usually folded during regular flight, but can be extended as well during soaring to aid in saving energy.
The patagium, or wing membrane, contains special elastic fibers that get harder in water to help the bat swim more efficiently.
The bat soars close to the surface of the water with the help of the wind currents like gannets. Once it sees its prey, it flies up in the air and the plunges head first into the water. With its prey in its mouth, it quickly swims towards the surface at high speed, and like a flying fish it hops in and out of the water several times until it gains enough momentum to start flapping its wings and fly.
This species of flying fox has adapted to hunting fish by plunging into water, just like gannets and other diving birds.
It has a highly adapted aerobic metabolism, with an unusual amount of mitochondria, capillaries, and cardiovascular system.
Its wings have a high aspect ratio for speed and soaring, as well as for saving the cost of flight.
Once it catches its prey with its mouth, it comes up to the surface by paddling its adapted hind limbs, which resemble those of other swimming mammals like sea otters.
In the surface it swims with its wings towards the closest shore, where it consumes its prey.
As part of the comparative study of the control of eye movements by secondary eyes, we will have to develop different methods for each species. For example, we have an eye tracker developed particularly for salticids. For other species, we will illuminate the retinas with IR light and then capture the reflection with an IR camera in order to see the movement. We will use eye-masking techniques, already developed in our laboratory, to understand the role of the secondary eyes, if any, in principal eye control.
Exploit renewable food source on riverbank (tides bring food). Maintain territory size all winter, don’t modify territory size in response to abundance of resources, instead they modify their behavior:
- If food is low, they get it from other place but return to defend territory.
- If food is abundant, they allow one subordinate bird (female or juvenile) to stay to help defend the territory because they can be kicked out later.
- If food is very abundant, defense is abandoned.
Gonad enlargement and ovarian development are driven by proximate factors, which are the external conditions that actually induce reproduction. Temperature is probably the most important modifier of annual gonadal cycles. Other factors such as habitat, vegetation, abundance of resources, or social stimulation help consummate the final stages of gonad enlargement and ovarian development.
New Caledonian Crows craft tools for probing and prying food. They make a variety of hooked tools by first selecting the raw material, then trimming it, and finally sculpting it into a hook. They also craft a second kind of tool from the leaves of a screw pipe by alternating angled cuts with horizontal rips to create a serrated edge. They use the tools for extracting insect prey from crevices.
Zugunruhe or migratory restlessness is determined by the circadian clock in response to the annual cycle. In a study of the orientation of Zugunruhe in Common Starlings, the birds were placed in cages in a room where they could see the sun, including its change of position as the day progressed. As long as they could see the sun, they focused their attention towards the northeast, the correct direction for spring migration. On overcast days, however, the starlings showed no directional tendency.
Following up on my work on sensory priming during the past semester and this summer, I will continue running arena trials with a new generation of P. princeps in order to study the behavioral responses of jumping spiders towards visual and acoustic stimuli. My experiments consisted of introducing a jumping spider in an arena so that it walked into a viewing chamber were pictures suddenly appeared in an iPod screen. The pictures were of a wasp (a potential predator), a cricket (a preferred prey), and a beetle (a neutral stimulus). Each spider was shown one image per trial and during the sound trials a speaker played a wasp buzzing sound for 5 seconds every 2 minutes. Since the trials were run between the end of the Spring semester and this summer, it is possible that the effect of age influenced the spider’s response towards the stimuli, because jumping spiders are very visual and still they showed little response towards the pictures.