sixty - two crayfish ( procambarus clarkii ) with rostrum - telson lengths of 7095 mm and maximum claw lengths of 1736 mm were obtained from carolina biological supply .
crayfish were housed individually in opaque plastic containers with shelters made of pvc pipe half - sections for two weeks before experiments began .
crayfish were examined to see if they were male , female , or intersex . in males ,
the first pair of swimmerets is long and prong - shaped and serves as a sperm - transfer organ .
females have a seminal receptacle located between the fourth and fifth pairs of walking legs , and visible oviduct openings at the base of the third pair of walking legs . of the 62 specimens , 49 were female and 13 were male .
since body size and claw size are intrinsic indicators used by crayfish ( bergman and moore , 2003 ) , we set up matches between male crayfish with similar telson - rostrum lengths and maximum claw sizes matched to within 10% . the two crayfish slated for a match were placed into an opaque - walled test arena ( rat cage ) 25  50  20 cm filled with clean water up to about 10 cm depth .
each of the two contestants was simultaneously placed in the tank , under a smaller shelter container .
matches started after 5 minute acclimation , when the small shelter containers were removed , and observations continued for up to 10 additional minutes .
matches were scored every 15 seconds , using the following table of behaviors from bergman and moore ( 2003 ) ( see table 1 ) .
the summed aggression over the match was calculated by adding up all the aggression scores for the duration of the match .
match duration was defined as the amount of time during which at least one of the two crayfish exhibited behavior that did not score a 0 according to table 1 .
match intensity was calculated by finding the mean aggression score over all the 15-second periods of the match .
jmp6 software ( sas institute 2006 ) was used to calculate t - tests and anovas .
after the matches , males either had their androgenic gland removed or had a sham surgery . after being anaesthetized in a bath of ice and water , male crayfish
the fifth pair of walking legs were each removed proximal to the opening of the vas deferens . using forceps ,
the androgenic gland , which is associated with the vas deferens , came out along with the vas deferens ( figure 1 ) .
sham surgeries were done as above , but forceps were used to root around in the base of the fifth walking leg , without removing the vas deferens and androgenic gland .
three weeks after surgery , crayfish were rematched and their summed aggression over the match , duration of interaction , and average intensity of interaction were calculated as before .
setting up and observing the matches and then performing the surgeries is doable in a typical three - hour undergraduate lab . in round one ,
our 12 male crayfish had a total of 23 matches . with six groups of students running matches
each surgery took about 10 minutes to anaesthetize the animal , followed by 530 minutes for the surgery ( still on ice ) , depending on the skill of the student .
all animals survived the fights and the surgery , although one male escaped and one male molted .
typically interactions started slowly , with little or no activity for the first couple of minutes , followed by approaches with and without meral spreads .
this was sometimes followed by increasing escalation to the point of hitting or grappling with claws .
unrestrained fighting was relatively rare . often , the crayfish disengaged after a couple of minutes and retreated to their own corners . while the results were not statistically significant , there was a decrease in mean total aggression from 17.3  5.2 to 8.1  3.8 after the removal of the androgenic gland ( t - test , p=0.13 , figure 2 ) .
the sham group showed no significant change in aggression ( t - test , p=0.51 ) .
crayfish matches were relatively short in length , ranging from 15 seconds to 9 minutes .
there did not appear to be any effect of and rectomy ( t - test p=0.76 ) or sham ( t - test p=0.83 ) on match duration , which was typically less than 3 minutes ( figure 3 ) .
again , while not statistically significant , there is a trend toward a decrease in the mean behavioral intensity from 1.04  0.5 to 0.39  0.27 after removal of the androgenic gland ( t - test p=0.21 ) , but not after the sham ( t - test p=0.79 ) .
students responded well to this lab . in an anonymous survey , students were asked to answer the following questions with numbers of 15 ( low - high ) .
 i have never really liked science , but this lab gave me a different overall experience . 
 i felt like it went above and beyond a normal lab setting for non - majors .
 aggression is something people deal with everyday so being able to quantify it in these crayfish was very fun and interesting .
 the students liked doing surgery , and they liked working with live animals , and they liked being able to relate what they saw to real life . despite the overall favorable experience , the lab could be improved technically and organizationally .
this process could potentially be facilitated by ablating the eyestalks a week or two before the initial fights and surgery ( khalaila et al . , 2001 ) .
this procedure causes the androgenic gland to hypertrophy , making it easier to spot during dissection
if possible , videotaping behavior and scoring behavior afterwards would lead to more consistent results and make possible the use of blind scoring .
additional factors that would have helped would have been to have the same teams score the same animals before and after the surgeries . on their own
the students were fully engaged , asking about putative hormone levels in aggressive world leaders and about emotional effects of steroids used as performance enhancers . while the lab did not produce statistically significant results this time around
, i believe that it is largely a matter of small sample size and inconsistency of scoring . in terms of student motivation , interest , and learning
 male procambarus clarkii were matched by size and largest claw length and observed interacting in pair matches before and after removal of the androgenic gland or a sham operation . although results were not significant , trends suggested that males showed less aggression after the removal of the androgenic gland . 
 average bout duration did not decrease , but mean intensity of interaction decreased . 
 this exercise was part of a student lab for non - majors . 
 students were positive about the lab , indicating that they learned about quantifying behavior , about hormonal involvement in aggression , and that the lab made them want to do more science . 
MATERIALS AND METHODS
RESULTS
DISCUSSION