Algebra 2: An Integrated Approach. Heath McDougal Littell. Algebra 2: Explorations and Applications. Algebra and Trigonometry, Book 2. Focus on Advanced Algebra. Scott Foresman Addison Wesley. California Algebra 2 Edition. Texas Algebra 2 Edition. Algebra 2 Edition. New York Math B. Advanced Algebra: Tools for a Changing World. Algebra 2 with Trigonometry. Advanced Algebra. Saxon Algebra 2 Free. Invasion Biology is no different and much attention is focused on the topic because, not surprisingly, invasive species tend to be very good at reproducing.
Green crabs are of course no exception, and biologists have long noted the proficiency with which the species can reproduce in new environments. These studies lay out the chemistry, anatomy, and behavior of green crab reproduction in fascinating detail. Notice how the 2 pairs of appendages work together, with the bottom pair acting as plungers for the top pair. First, an anatomy lesson. Male green crabs use two pairs of specialized reproductive appendages for mating Spalding These appendages, nestled delicately beneath the hard abdominal flap, are essentially modified legs.
The first pair are long and hollow, like the barrel of a hypodermic needle, while the second pair are smaller and act like plungers. Together these appendages form twin gonopods and act like a sort of double barrel injection system.
One would not be faulted for thinking of these as penises, but actually the penises yes, plural are just small, fleshy nubs at the base of each gonopod that load this injection system with spermatophores.
Each spermatophore is a cocktail of sperm, fluids, and a sticky chitinous substance that acts to hold everything in place once embedded in the female.
Inside the abdominal flap of a female green crab. Notice the two distinct gonopores and multiple feathery appendages. The female reproductive anatomy, by contrast, is somewhat cryptic. Beneath the broad abdominal flap are layers of feathery appendages — again, modified legs — that will eventually provide an attachment point for extruded eggs. The only reproductive organs visible are the large paired gonopores that reveal the opening to the two vaginas Spalding Internally though, things are much more interesting, with each vagina opening up into an enlarged chamber called the spermatheca, where the spermatophores will eventually be deposited.
Female crabs can store sperm for a year or more within the spermatheca and may produce multiple clutches of eggs from a single mating. Mating in green crabs is complicated. After all, an armored shell is great for defense but it makes sex awkward, if not impossible.
Females must be in a newly-molted, soft condition in order to copulate. Thus, timing is everything. The smell of a ripe female can send males into a frenzy and competition often gets violent, frequently resulting in injury. Larger, older males are more aggressive than their smaller, younger counterparts, and tend to win these contests and drive away rival suitors. Interestingly, females also favor bigger males when given a choice Sneddon et al. In these situations, the female may fall backward exposing their abdomen while performing an abdominal flapping motion for a minute or more, before sidling up beneath the male.
Male European green crab grasps the female in the pre-copulatory embrace. This behavior may continue for up to two weeks. Once the male grasps the female in the pre-copulatory embrace, they will remain that way for up to two weeks. When the female signals her molt is imminent, the male releases her briefly, only to grasp her once again in the copulatory embrace.
Now upside down, the female holds herself in place with the tips of her walking legs. Whereas for many creatures, the actual act of sex is a fleeting sprint, crab sex is a marathon. On average, green crab sex lasts more than 2.
Typically, the couple find a secluded spot during this time to avoid disturbance, which is critical not only to avoid interruption but to protect the female; with her shell not fully hardened, she could easily be damaged by another male or a predator. In fact, once mating is completed, the male will continue to hold the female in a post-copulatory embrace to provide additional protection in a behavior called mate guarding Christy Eventually the male releases the female and the two go their separate ways.
With abdominal flaps open, male and female green crabs mate face to face, often for over 2. For biologists, mating systems like this are extremely interesting for evaluating evolutionary questions. If a male releases a female too early, then she will most likely mate again, and male copulatory systems are well-adapted to thwart rival sperm.
The shape of the gonopod, which is strongly curved Clark et al. Less is known about how female green crab influence this competition, although research in other species, including Dungeness crab Jensen et al. While these new discoveries can be fascinating in their own right, understanding the details of how, when, and where green crabs find mates and reproduce can be incredibly helpful for developing successful approaches for management.
For instance, researchers are already hard at work developing artificial sex pheromones that may someday help us attract frisky crabs before they mate. Every new discovery gives us biologists more to think about and could give managers more tools to control invasions. If you have any questions about any of the works cited here, please feel free to reach out to crabteam uw. Back to Contents. Do you know your sculpins?
Photo courtesy of Mark Wegehaupt. Species Name : Oligocottus maculosus. Geographic Range: Southwest Alaska to southern California. Service projects or work weekends may fit this description.
Part C is to be completed and signed by a certified and licensed heath-care provider—physician MD or DO , nurse practitioner, or physician assistant. Part D Part D is required to be reviewed by all participants of a high-adventure program at one of the national high-adventure bases and shared with the examining health-care provider before completing Part C.
Guide to Safe Scouting View. The purpose of the Guide to Safe Scouting is to prepare members of the Boy Scouts of America to conduct Scouting activities in a safe and prudent manner. The policies and guidelines have been established because of the real need to protect members from known hazards that have been identified through years of experience. Limitations on certain activities should not be viewed as stumbling blocks; rather, policies and guidelines are best described as stepping-stones toward safe and enjoyable adventures.
Incident Information Report View. Events or allegations of injury, illness, or property damage including employment and directors and officers issues. Talent Release Form View. Tour and Activity Plan View. This form can also be filled out and submitted online through your MyScouting account.
At the North Valley recharter day in January , these scorecards will be used to determine the level your unit achieved in the Journey to Excellence.
Journey to Excellence View. National's Journey to Excellence website. This site contains all of the information available about this program.
Website to record service hours for Journey to Excellence. Cubmaster's Key Progress Report View. This award has replaced the Cubmaster Award, which has been discontinued and can be earned by any Cubmaster. It can be earned in each position, but tenure may be used only for one award.
This award can be earned by any registered adult leader in a Boy Scout Troop. This award has replaced the former Cub Scouter and Pack Trainer awards, which have been discontinued. It can be earned by any registered adult leader in a Cub Pack. Scoutmaster's Key Progress Report View. This award can be earned by any Scoutmaster.
Unit Leader's Award of Merit View. Quality unit leadership is the key to a quality unit program—and it leads to better Scout retention. A quality Scouting experience will help keep Scouts in the program, and the Boy Scouts of America created the Unit Leader Award of Merit to recognize the quality unit leaders who make that happen. This new recognition has revised requirements, and Cubmasters are also eligible for this recognition.
The Boy Scouts of America specialty plate is designed to raise community awareness. Scouting Certificate Wizard View. Webelos have different requirements for the Supernova Award. Nova Awards Program Overview View. The instructor-led course is designed to be used with the STEM Orientation slide deck at roundtables and other training events.
Supernova Award Application View.
0コメント