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University of the Pacific Theses and Dissertations Graduate School
1979
Sexual dimorphism, resource partitioning and intraspecific aggression in Caprella californica Stimpson
Ian D. Campbell University of the Pacific
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Recommended Citation Campbell, Ian D.. (1979). Sexual dimorphism, resource partitioning and intraspecific aggression in Caprella californica Stimpson. University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/ uop_etds/1996
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SEXUAL DIMORPHISM, RESOURCE
PARTITIONING AND INTR.l\SPECIFIC AGGRESSION IN CAPRELLA
cal:Lfornica Stimpson
----- A thesis presented to the Graduate Faculty of the
UNIVERSITY OF THE PACIFIC
In Partial Fulfillment
of the Requirements for the Degree
MASTER OF SCIENCE
by
Iah D. Campbell
August 1979 l'l•.
· This thesis, written and submitted by
Ian D. Campbell is approved for recommendation to the Committee on Graduate Studies, University of the Pacific. ------. .
Department Chairman or Dean:
Thesis Committee:
Chairman
,------
;=;- = -=---o "-"--'=------='-----'-'------'
Dated~------
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,...------t::":"-- 1 ~ f-'j-- s~-==-= ::
I would like to express my warm appreciation to all my fellow students at the Pacific Marine Station, especially John Brezina and Joe Mendoza, for their invaluable help on this manuscript. To my two best friends, my wife Margo and my father Robert, I want to say thanks for everything. Without these friends none of this would have been possible.
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INTRODUCTION
~~--- R''"'" nm,.mm The Caprellidae are a specialized suborder of ~
Amphipoda, which are highly modified for a semisessile
life. Caprellids exhibit direct development and brood
their young. The suborder is exclusively marine and
commonly found on filamentous algae, sea grasses and
c f-; fouling communities. Most published works on caprellids r::;------~------
,__._~ ______have been primarily concern~d with systematics (Caine, 1974; ~------i' i" ... Dougherty, 1943; Laubitz, 1970, 1972; McCain, 1968, 1975),
although a few recent studies have dealt with ecology and
ethology (Bynum, 1978; Caine, 1977; Keith, 1969, 1971;
Lewbel, 1978; Saunders, 1966).
This study examines·spatial and temporal variations
in distribution, abundance and population structure as well
E~~----==: as describing intraspecific aggressive behavior of Caprella .~ ~---=--~----,----=-=------=---
~- - ~- californica Stimpson. ~- californica is dioecious and has
marked sexual dimorphism in both its size and secondary sex
characteristics. It is found from San Diego to the South
China Sea (Laubitz, 1970), and is the dominant caprellid
in the Zostera marina beds of the local bays and is a
major diet item for many of the eel grass associated
fishes. There is a preponderance of females in the
population as well as a size-specific distribution of the
proportion of the sexes. ~------2 ,,_ t:fF ___ _ t-c-
MATERIALS AND METHODS
SAMPLE COLLECTION
Samples were collected in Tomales Bay adjacent to H Lawson's Landing Resort during a one-year period from
February 1978 to January 1979. Samples were taken every other month for the first six months and monthly there- after. Three 2 m squares were sampled near the center of a large Zostera marina bed. Six random samples were taken within each square .every period. Each sample consisted of a "handful" of ~·marina carefully removed from the substratum.
These were placed in separate 3.8 liter plastic bags along with 10% buffered formalin in sea water. Removal of caprel- lids from the eel grass was accomplished by filling sample bags half full of water, agitating, removing strands of z. marina and pouring the contents through a 0.5 mm sieve. This ~=-=-=--=,: =-=--- procedure was repeated several times for each sample. Eel p_-----:----:----
E- -~---- grass was later examined under a dissecting microscope to ~- ensure removal of all caprellids. The length of the Z. marina strands in each sample was also recorded.
SAMPLE ANALYSIS
Secondary se~ual characteristics were used to differ- entiate the sexes. Adult males possess a conspicuous second t gnathopod, while adult females have marsupial plates r (oostegites). In immature females, these plates appear as ------,_
3
small evaginations near the gills. Individuals lacking
the above characteristics were classified as juveniles.
Since the total length of preserved caprellids was
difficult to measure, the second pereonite was measured to
the nearest 0.1 mm with an ocular micrometer. A signifi-
cant linear relationship (Regression p < 0. 001) was found . / between pereon1te 2 and total body length for both sexes
(Fig. 1). Eggs were removed from fecund females and ~--~- g_ ------1, ct.:_ __ counted. 6---=--- ~ Over 3200 Caprella californica. were sorted during the
course Df the year. These provided data on relative
abundance, sex ratio, proportion ovigerous females, percent mature fe.males, percent juveniles in the population, and monthly size frequency distribution.
LABORATORY EXPERIMENTS AND BEHAVIORAL OBSERVATIONS ~-== Collections ~c~------
Living specimens of Caprella californica were collected with a dip net from the Zostera beds near the mouth of
Tomales Bay. The organisms were placed in glass jars with
cut eel grass and sea water for transportation. In the
laboratory. they were placed in glass aquaria and supplied
with running sea water.
Experiments
Two experiments were performed to determine vertical
distribution of C. californica on the eel grass substrate. i 4 ~===~
In the first, sediment from the area of collection was spread approximately 5 em deep in a glass aquarium. Twenty single strands of freshly cut Zostera marina were attached r-~H ~·~~-= to a 1/4 in. dowel which was buried in sediment. The eel H grass extended 32.5 em (approximately equal to mean thallus length for February-March) from the sediment (Penny, 1978).
The Z. marina was scraped off with dry paper towels to
remove encrusting organisms ensuring that food availability ~--~
H--~---- didn't affect caprellid distribution. One caprellid per 5------ii strand, 10 males and 10 females, was placed into the tank and left for 24 hours to assure natural distribution on the sea grass. This population was changed approximately every three days. Fresh filtered sea water was circulated contin- uously for the duration of the experiment. A total of 204 measurements were made over a three-week period. Caprellid sex, position, movements and numbers .per strand were recorded.
~:-_: ___-:______:_=--- The vertical distance from the substratum to the caprellid's '------~------=-=--- abdomen was used as the height measurement.
A second measurement was designed as a two-factorial
;::::-:-:--.-.. -·-- analysis of variance (ANOVA) with sex and condition of eel grass as factors. The design was similar to the above experiment except that 40 strands were used. The four conditions of eel grass consisted of: 10 strands scraped as above, 10 inverted unscraped strands, 10 unscraped
~---- strands, and a combination of the previous three. One
~--.-- caprellid was placed on each strand with five males and ------5 i···· five females per condition, and left for a 24 hour period.
Sex and vertical distribution were recorded consisting of a total of 280 data points.
A third experiment was designed to investigate the strong intraspecific agonistic behavior of C. californica.
The main design was the same as above. Twenty single strands and 20 caprellids, one per strand, were placed in
>------~------a glass aquarium. Five of the 10 introduced males were P- rJ. ------b; --- in a 2.0 to 3.0 mm size class with the remaining five in ~--- !' i· a 3.5 .... 4.5 mm size class (based on pereonite 2). All of the introduced females measured less than 2.0 mm.
Observations on aggressive behavior were made eight times over a three-week period totaling 146 individual encounters. An "encounter" was defined as physical contact
by one individual caprellid eliciting an active response ~ ~ ------by another. Each encounter was scored by sex of combatants, size of aggressor (aggressor was defined as the individual in motion or approaching at the time of contact) , type of attack and type of response (antennae or gnathopod). Other variables also recorded were which individual won or lost, subsequent movement of loser, and the resulting orientation of the combatants to each other.
;,_; ___ _
=~~-~= 6
RESULTS
COLLECTIONS
Relative Abundance
. Fluctuations in monthly relative abundance over the course of the year followed a pattern typical for other temperate caprellid species (Bynum, 1978). Fig. 2 shows
that the population experienced low relative numbers in the ~ R------H winter months followed by a rapid increase in the spring and ,bi - --- n--~-- early summer. The lowest relative abundance figures were !l recorded in April 1978 and December 1978, and the highest values in September 1978. During the one-year sampling period, the grand mean of monthly relative abundance was
2.149 (S.E. ~ 0.308) caprellids per linear meter of
Zostera marina. According to Bynum, when the substrate is dense (late spring, summer and fall), these abundance 1"--~ ~~ ~--- figures accurately estimate density but may overestimate it when the substratum is less evenly distributed (i.e., winter) .
Sex Ratio
There were 43.21% males in the population summed for all collections. A chi-square test (Table 1) indicates that the difference from 50% is highly significant (p < 0. 005) . !
Differential mortality is-often used to explain such devia- tions and while this may occur here, further study is .. ------l..". 'L 7 '·g;:u ---·--••• necess~ry to verify this. The lowest mean proportion of males occurred in February 1978 (Fig. 3) and the highest was found in Octobe!r 1978. The large proportion of males in October closely followed high juvenile recruitment in
September 1978 (Fig. 8) and may indicate that more young males entered the adult population that month than did young females.
The percent males in each size class, summing for the R------~
~ ------entire year (Fig. 4), showed that the smallest (one through ~ ---=-=------=------four) size classes ~onsisted of mainly females. In size class five (2.0- 2.3 rnrn), the proportion of males is 57.63% and this proportion continues to increase rapidly reaching
100% by size class 10 (4.0- 4.3 rnrn).
Reproduction
ovigerous females were encountered during the entire e===·_._·==-=.. = ~ sampling period (Fig. 5). This suggests that Caprella californica does not cease reproducing during the winter as do many temperate marine invertebrates. Nine-point- four-two percent of all females and 12.11% of adult females were ovigerous when summed for all collection. The highest n=== number of gravid females was in April 1978; in January 1979 no gravid females were seen. Examination of the data indicates that there has been an apparent decrease in female productivity during the year sampled. 8--- ~ A regression analysis of the relationship between egg number and female size (using pereonite 2) was found to be 8
highly' significant (p < 0.001, Fig. s). The relationship
between size class and number of eggs appears in Fig. 7 • t~ nn unnnnnn
The smallest individuals had the smallest brood size and ~--
vice versa; the average number of embryos per female being
36.025 (S.E. + 3.852). Since size was found to be a signi-
ficant factor in caprellid fecundity, the distribution of
ovigerous females in each size class was investigated. The
majority (50.64%) was in size class three (1.2 - 1.5 rnm) ~------~ ~-~------· with only 1.92% gravid females outside the size 6lasses t ------ ri I• three, four or five. It appears that £• californica females i
reach reproductive maturity at ~pproximately 1.2 rnm (pereonite
2) since only one ovigerous female was encountered below
that size (1.1 rnm).
Recruitment
Juveniles were present during the entir~ year with the
[:: __ _ exception Of December 1978 (Fig. B). The winter months were
characterized by low numbers followed by an increase in
spring and reaching high numbers occurring by mid summer.
The highest proportion of juveniles in the sample population
was in September 1978 which also corresponded to the lowest
mean size values for both males and females. The lowest
percentage was in December 1978 where no juveniles were
encountered.
Prereproductive females (females not having fully
developed oostegites) followed the distribution of juveniles
. closely but with a one-month lag (Fig. 8). The low L i ~ t ~ 9 b~'= proportion of ovigerous females in October 1978 may be due to the influx of young females during this month.
Size Distribution
Monthly size frequency histograms with a size class interval of 0.3 rnrn were constructed yielding 15 groups
(Fig. g). The largest males fell into size class 15
(pereonite 2 from 6.0 - 6.3 rnrn) and the smallest juveniles into size class one (0.4- 0.7 nun). The percent distribu- E; ____~- "r-1 h tion was computed for each class using monthly means as well '~------[' ____ _ rfC as the pooled data (Fig. 10)". Data on monthly mean lengths i are summarized in Figs.11a and 11b.
The male histograms showed a bimodal distribution during several winter months indicating the presence of large "over wintering" males. These large males disappear by summer
(June) and occur again at the onset of the hext winter ~ I] (November). No such bimodality was apparent for females. ~=--o======~ ~ ~ The trend in males was not consistent enough to make deter- mination of growth rate possible. The greatest number of females occurred in size class three (1.2 - 1.5 rnm) and no - =---=---=::------=-=- ,...; females were found larger than class eight (3.2 - 3.5 rnm). ~---
The largest number of males were in size class five (2.4 -
c ------~~ - ~--~- 2.7 mm) and gradually decreased in proportion to class 15
(6.0- 6.3 rnrn). A dip in percentage in class four may ihdi- cate a strong selective pressure acting on that particular size class (i~e., size specific predation).
The data on monthly mean length exhibited a seasonal trend in both sexes (figs.11a and11b). The largest 10
individuals as well as the highest means were recorded in
the winter months with the lowest rne~ns falling in the
summer. A 3-t·lAY ANOVA was performed (Table 3) with months,
sexes and size classes as the factors that indicate signi-
ficant differences between sexes and size classes but no
difference- between months.
LABORATORY OBSERVATIONS
Vertical Distributions
In the first experiment, the data showed a differerttial
preference in vertical distribution due to sex. The females
tended to accumulate in the upper two-thirds of the thallus.
After the first 91 measurements were obtained, it was found
that 88.9% of the females were above 10 ern. Conversely,
43.5% of the males were found to be in the bottom 10 em.
A simple one-way analysis of variance (ANOVA) was made of the populations of males and females (Table 3).
The between-sex variation was found to be highly significant
(p ~ The other data on movement, associations and directional ~=~=--====-===--= orientation provided the following: 1. 87.5% of the individuals in motion at the time ·t of measurement were males. B -==--=- ='----=----=- 2. A majority of both males (67.2%) and females (63%) were aligned positively on the Zostera r.----=-----_-- thallus. ------ 3. Of 40 associations recorded, only 17.5% were :; r~ l' 11 ~= male x male, while 47.5% were male x female, and 35% were female x female. In the second ~experiment a two-level factorial ANOVA was performed on the data (Table 4}. The treatment effects of eel grass condition was found not to be significant while sexes was highly significant (p < 0. 001). This result indi- cates that nothing on the !· marina strand itself seems to cause the differential distribution in C. californica. Intraspecijic Agonistic Behavior Attack and Response There appea.r to be two methods of attack behavior in Caprella californica. One is to attack using only the antennae and the other to use both antennae and secondary gnathopods. There is an apparent difference here between the sexes, with the females much more apt to respond to ~------ i"===::i-= ______:_--:.;::..=______- aggression with their gnathopods. In male vs. male combat the receiver responded to attack with its gnathopods in only 10.39% of the cases. In male vs. female encounters, the females responded with gnathopods 69.35% of the time. ~------ On the aggressive side, in male vs. male "fights," males 6------used only antennae 85.71% of the time and 62.90% in male p vs. female episodes. Apparently the most important factor causing a particular response is the method of attack, with 98.48% of the receivers in male vs. male cbntact and 62.90% ~~----- in male vs. female incidents responding the same as the aggressor. 12 Final Orientation of Individuals There are four different attitudes that can_be taken by the pair of individuals following an encounter: 1) both facing toward the other, 2) both turned away, 3) the winner facing the loser, the loser facing away, and 4) the loser facing the winner, with the winner turned away. There seems to be a fairly even distribution of these outcomes with the exception of the final one (Figs. 12 a and 8E------ r~ 12b). Only in a very few cases was it found that the loser [ was facing the winner who was facing away (1.40% in male vs. male and 3.77% in male vs; female). Combat Success In male vs. male combat, being large or aggressive (the approacher) had a significant relationship to winning '-"--- the encounter. The "successful" individual was the one that hl~---~ccc_-- caused the opponent to move away immediately following the interaction. The large male won 76.00% of its combat inci- dents and the aggressive male was victorious 78.18% of the time. Combining the two characteristics, large and aggressive, the combatants were successful in 81.48% of the ~------ "~ "fights." Conversely, size and aggressive nature was not an advantage in male vs. female combat. The males were all ;;: -- larger than the corresponding females and were also always ,_. ______- the "aggressor" since females remain stationary a majority h - ::::_-~-·::_-~-- of the time. Males only were successful against females in 13 ~ ---. ;;;· 48.21% of the cases. A three-way contigency analysis was performed with success as a function of size and initiation of endounter (Table 5). Size and aggression were found to be inde pendent, implying that sizes of males do not differ in aggressive behavior. The test of independence between size and combat success is significant (p < 0. 01) indicating that winhing is dependent on the relative size of males. The test of_independence between success and aggression was also significant (p < 0. 001) , implying either that there is a correlation between aggressive nature and the probability of success or that initiation of combat is an advantage of the individual aggressor. Disposition of Loser h ::: __.:______-::.._.-=--- Aggression is often associated with territoriality but this is apparently not the case in Caprella californica. This species is very aggressive but does not appear to drive the dominated individual away. The aggressor in these com- bats drives the receiver off the Zostera thallus 46.48% of the time in male vs. male incidents and 45.28% in male vs. female encounters (Table 6). It is interesting to note that ti~- ...... even though the female is always the "receiver," she drives the male off the eel grass thallus in 66.67% of the contacts ~---- that she wins. Male "receivers" drive off 44.44% of the losers. 14 DISCUSSION ~ ~-~-~- --~~-- The causation of sexual dimorphism has been the center R of intensive study since Charles Darwin coined the phrase "sexual selection". Darwin felt that intersexual differ- ences were a result of competition among members of one sex for access to the other sex (Kolata, 1977). Robert Trivers (1972) suggests that the key to control of sexual selection can be found by ex_amining "parental investment". He states that which ever sex invests the most in their offspring will b~come a limiting resource and as such will be competed for by the opposite sex. Caprella californica is a polygonous species with a large female "parental investment" (egg brooding). Large size in male has generally .been attributed to this intrasexual competition for females (Aldrich, 1974; Carefoot, 1973, Ghiselin, 1974; Ralls, 1976; Shine, 1978}. Males will be large whenever increased size confers some advantage in intrasexual compe- tition, with the largest animals being inordinately "---;::--.:------=::--~--- successful and having a higher proportion of mates (Ghiselin, 1974; Kolata, 1977}. In C. californica sexual dimorphism with respect to size is pronounced with males by far the larger sex (Fig. lOa,b). Intrasexual male combat is, also characteristic o=------with the largest individuals more successful than their 15 smaller counterparts. Mating episodes were never observed in the laboratory and males did not appe.ar to defend a specific territory. The successful males may improve ~···,, r~ reproductive success by displacing any rival that they encounter; thus increasing their chance of being the first to mate with available females. In fact actual combat between males for possession of individual females seems to be a rare event in nature (Mayr, 1972). nli ------G Ralls (1976) suggests that the degree of dimorphism pcr_--- H is a result of the difference of additive selective !' pressures affecting size in males as compared to those in females. Also, due to their relationship to the following generations females have a more narrow range of ways to increase their Darwinian fitness than males (Ghiselin, 1974). The females appropriate manuever is to invest in increasing ~------ !~ the quantity and quality of their offspring. According to ~------ Ghiselin, the amount of energy necessary for sperm pro- duction leaves males with an excess that might be directed towards other males, monopolizing mating opportunities or defending ·territorial resources. He feels that females are ~ ------=----- adapted to survive while males are adapted to reproduce more than other males. Animals that engage in sexual combat have developed many physical and behavioral mechanisms to reduce severe injury. Caprella gorgonia Laubitz and Lewbel actively use their second gnathopods during male combat to "grasp and ~ : l-~ 16 b----- pinch" one another and this behavior is a "significant cause of mortality" (Lewbel, 1978). To reduce the obvious risks of continual aggression, agonistic behavior el-- is limited to mating episodes. Caprella californica on the other hand does not limit intrasexual combat to mating but reduces risks by another strategy.· Male combat is "ritualistic" and the use of second gnathopods is rare. The ,, animals threaten each other, grapple for a short time using E ------0__ mainly antennae but actual injury was never encountered in [' -- - 1;;- r· the laboratory. I' I i Intersexual aggression is also a characteristic of c. californica. Laubitz (1970) describes the sec6nd gnathopod in females as containing a "poison spine" not mentioned for males. Upon contact with a male, females actively respond with this gnathopod and are in most cases the dominant individual even-though they are smaller. Ralls (1976) feels that such female dominance may have evolved to avoid being treated as a male diet item and to protect the young. Caprellid cannibalism was observed in the o-;~--- !:.:: laboratory and has been documented by Saunders (1966) and Keith (1969). According to Stein (1975) females resisting mating attempts by males has other "survival value". Only >; ...... tl . - large dominant males will be successful in copulation ~·--- -··- allowing females to pass on traits that will result in greater fitness. ---- ~ .. ~~ 17 b======Hate selection or "female choice" may be an important factor in the development of sexual dimorphism in this species •. Male combat and female choice actually may not be separate strategies but one and the same (Ralls, 1976; Schoener, 1968; Trivers, 1972). "When a selective advan- tage is linked to a secondary sexual characteristic there should be a simultaneous selection of the preference of the other sex for this advantageous type" (Ralls, 1976). Female choice may be! active, as above, or it may be relatively passive. Since females r~main stationary a majority of the time males that attempt to copulate with them may have already been successful in numerous combat incidents thus establishing a case for their reproductive abilities. Intersexual bbdy size differences are a result of selective pressures acting on both sexes (Ralls, 1976; c.: __ Shine, 1978). Carefoot (1973) suggests that smaller relative female size is caused by the energy requirements of reproduction. In Caprella californica these energy requirements involve the development of oostegites and the ----- t:-···- subsequent brooding of the eggs and young. In other caprellids (~. gorgonia, ~· laeviuscula, and Metacaprella kennerlyi) larger females do not produce more eggs than smaller ones, indicating that smaller size is not a function of the energy spent on egg production (Lewbel, "-- f' 1978). C. californica does show a significant relationship p t ~ 18 [ ____ ~- between female size and egg number suggesting that size and energy requiremEmts of reproduction may be correlated. w --- The males of ~· californica may delay sexual development in ~ order to put more eriergy into growth since ~ize may be a selective sexual advantage, and the females may improve their fitness by developing quickly_and reproducing early (Ghiselin, 1974; Ralls, 1976). Kolata feels that small size may evolve in cl fluctuating environment in which it is advantageous to breed quickly. c. californica as well as most caprellid species, live in s·uch an environment (Bynum, 1978; Laubitz, 1970; Lewbel, 1978). Resource partitioning or differential niche utilization has also been cited as a major contributing factor in the causation of sexual dimorphism (Ghiselin, 1974; Mayr 1 1972; Rand, 1952; Selander, 1966; Storer, 1966}. · Dimorphism can be either structural or behavioral and has usually been t...: ------ attributed in part to the decrease in intersexual competi- [::- tion for food resources and a resultant increase in species carrying capacity (Andrews, 1974; Fleming, 1975; Ralls, 1976; ~---- Schoener, 1967}. In Caprella californica the sexes partition their structural habitat with the females occupying a higher vertical position than males. Fleming (1976} points out that if the sexes occupy different structural subniches, then intersexual competition will decrease and the selective pressure for physiological dimorphism will disappear. Gut 19 contents of similar sized males and females of C. califor- ~ica showed little difference in diet. Although a small proportion of the males contained a low percentage of crustacean parts this lack of difference seems to indicate that structural dimorphism in this species is not an adaptation to decrease intersexual competition for food. c. californica appears to use a behavioral dimorphism to reduce this competition for food resources. B------lei f-:--- Behavioral or size difference between the sexes in I..: ------r;G I ~ this group could make one sex more visible to predators !: that forage visually. According to Lewbel (1978), the coloration and the "move and freeze" behavior indicates that predation pressure has been important in the evolution of caprellids. Several species of fish fou~d in Tomales Bay feed heavily on caprellids (Brezina, 1979: Bane, 1972; t..: ,. Quast, 1968) and selective predation may account for the c ------=- female skewed sex ratio of this group. Maley (1970) feels that in a prey species with sexual dimorphism, a predator may be able to see the difference and eat more of one sex. ------ E ------Males and females have different life habits such as mobility or coloration allowing one to escape predation more often (Wenner, 1972). In c. californica males are in motion more often and are larger than females. Prey motion and E- . visibility are the most important factor in many fish I foraging strategies (Zaret, 1975). Giesel (1972) feels u 20 c r=--===== that species with higher male mortality would be better i ..... able to track short term changes in the environment, have greater niche widths, and would be more efficient colonizers. ~l=i ------F So the selective pressures in Caprella californica to H escape predation by remaining motionless may be less important than other genetic pressures. ...------~--~ IJ -- "P--· L:_ p- ~-;- E_: __ c-, __cc __ :-_ ~----__ 21 LITERATURE CITED Aldrich, J.C., 1974 Allometric studies on energy relationships in the spider crab Libinia emarginata (Leach) • Bio. Bull. mar. biol. lab~ Woods Hole, Vol. 147, pp. 257-273. Andrews, R.M., 1971 Structural habitat and time budget of a tropical Anolis lizard. Ecology, Vol. 52, pp. 262-270. Bane, G.W. and A.W. Bane, 1971 Bay Fishes of Northern California. Mariscos Publications, N.Y. 110 pp. Brezina, J.E. 1979 Part 1. Diet and growth of two juvenile flatfish, the English sole (Parophrys vetulus) and Speckled "ti------~------ [-:-- sanddab (Citharichthys stigmaeus), on a California p--- ~ sandflat. M.Sc. thesis, University of the Pacific, Pacific Marine Station, Dillon Beach, California, 83 pp. Bynum, K.H., 1978 Reproductive biology of Caprella penantis Leach 1814 (Amphipoda: Caprellidae) in North Carolina, U.S.A. Estuarine and Coastal Marine Science, Vol. 7, pp. 473-485. f--: l; L 22 ~====== Caine, E.A., 1977 Feeding mechanisms and possible resource partitioning of the Caprellidae (Crustacea; Amphipoda) from Puget Sound, U.S.A. Marine Biol. Vol. 42 no. 4, pp. 331-336. Caine, E.A., 1974 Comparative functional morphology of feeding in three species of Caprellids (Crustacea; Amphipoda) from the ~- northwestern Florida Gulf coast. J. Exp. Mar. Biol. n -- " Ecol., Vol. 15, pp. 81-96. n_-f:1 ____--- i"· r Carefoot, T.H., 1973 I i Studies of growth, reproduction, and life cycle of the suprali~toral Isopod Ligia pallasi. Marine Biol. Vol. 18, pp. 302-311. Dougherty, E.C. and Steinberg, J.E., 1953 Notes on the skeleton shrimps (Crustacea: Caprellidae) ~- -- E;_ ·- ··---- · of California. Proc. Biol. Soc. Wash. Vol. 66, pp. ~- - ~--- 39-50. Fleming, T.H. and R. s. Hooker, 1975 Anolis cupreus: The response 6f a lizard to tropical .• t:- -- -~-- --- seasonality. Ecology, Vol. 56, pp. 1243~1261 • Ghiselin, M.T., 1974 E -=-=------==== The Economy of Nature and the Evolution of Sex. University of California Press. Berkeley, California. 368 pp. Giese!, J.T., 1972 Sex ratio, rate of evolution, and environmental ; ~ f; 23 ~- . - "' heterogeneity. Am. Nat. Vol. 106, pp. 380-387. Keith, D.E., 1969a Aspects of feeding in Caprella californica Stimpson and Caprella equilibra Say (Amphipoda). Pacific Science, Vol. 25(3), pp. 119-124. Kolata, G.B., 1977 Sexual dimorphism and mating systems: How did they :. evolve? Science, Vol. 195, pp. 382-383. 8. L~ubitz, D.R., 1970 ~=---~ Li --- - A Studies on the Caprellidae (Crustacea; Amphipoda) of }! the American North Pacific. Publ. in Biol. Oceanography, n~ 1, Nat. Mus. Canada. pp. 1-89. Laubitz, D.R., 1972 The Caprellidae (Crustacea; Amphipoda) of Atlantic and Artie Canada. Publ. in Biol. Oce~nography, no. 4, Nat. Mus. Canada. pp. 1-82. . ~F:===== L;__ ------d ~ .. ------ Lewbel, G.S., 1978 ~- Sexual dimorphism and intraspecific aggression, and their relationship to sex ratios in Caprella gorgonia· (Laubitz and Lewbel)~ J. Exp. Mar. Biol. Ecol., Vol. ~ :-~---~:-___-- ____ _ 33, pp. 133-151. Maley, E.J~, 1970 The influence of predation on the adult sex ratios ~H of two copepod species. Limnol. Oceanogr. Vol. 15, pp. 566-573. 24 Mayr, E., 1972 Sexual Selection and Natural Selection. In B. Campbell, ed., Sexual Selection and the Descent of Man. pp. 106-135. Aldine, Chicago. McCain, J.c., 1968 The Caprellidae (Crustacea; Amphipoda) of the North Atlantic. BullE~tin, u.s. National Museum, No. 278: lj pp. 1-147. ~---- g·~ .· Quast, J.C., 1968 ~-- n,, Observations on the foo.d of the kelp-bed fishes. In, i Utilization of Kelp-bed Resources in Southern California,· edited by W.J. North and C.L. Hubbs, Fish Bull. Calif. Vol. 139, pp. 109-142. Ralls, K., 1976 Mammals in which females are larger than males. Quart. Rev. Biol., Vol. 51, pp. 245-276. L:------ ~ - -- Rand, A.L., 1952 ~--- Secondary sexual characteristics and ecological competition. Fieldiana. Zool. Vol. 34, pp. 65-70. Saunders, C.G., 1966 Dietary analysis of Caprellids (Amphipoda) • ~ Crustaceana, Vol. 10(3), pp. 314-316. !j ------ Schoener, T.W., 1967 The ecological significance of sexual dimorphism in size in the lizard Anolis conspersus. Science, H~- ~ Vol. 155, pp. 474-477. 25 ·schoener, T.N., 1968 The Anolis lizard of Bimini: Resource partitioriing in a complex fauna. Ecology, Vol. 49, pp. 704-726. Selander, R.K., 1966 Sexual dimorphism and differential niche utilization in birds. Condor Vol. 68, pp. 113-151. Shine, R., 1978 Sexual size dimorphism and male combat in snakes. [,j t----~------Oecologica, Vol. 33, pp. 169-277. R---R F: i Stein, R.A., 1976 i Sexual dimorphism in crayfish chelae: functional significance linked to reproductive activities. Can. J. Zool., Vol. 54, pp. 220-227. Storer, R.W., 1966 Sexual dimorphism and food habits in three North American Accipiters. Auk. Vol. 83, pp. 423-436. c __ _ ~,., ...... - Trivers, R.L., 1972 \=0- -- Parental investment and sexual selection. In B. Campbell, ed., Sexual Selection and the DesGent of ::::;----. Man. pp. 136-179. Aldine, Chicago. Wenner, A.M., 1972 Sex ratio as a function of size in marine Crustacea. Am. Nat., Vol. 106, pp. 321-350. Zaret, T.M. and W.C. Kerfoot, 1975 Fish predation on Bosmina longirostris: Body size selection versus visibility selection. Ecology Vol. 56 I PP• 232-237. p [ ____ ~------~ c::_-==-- = ~= Figure 1. R- ~ ; Regression line showing the relationship between I the length of the second pereonite and the total caprellid length (to the nearest 0.1 mm.). Solid line based on 180 male measurements. Regression equation: Y=3.37x + 4.48. Slashed line based on the same number of female points. Regression ~- - - equation: + 1.82. ~------_ Y=4.44x E:; !o.::_-~:::____::_c_ ~ -- :::;----_-: ;...;-~------E-~ ------ s- --=-=--- .---~------ 1 7 1 6 1 5 1 4 1 3 I ? 1 2 ~ - / .1: I E 1 1 / - / 1 0 / :t: // 1- . 9 G // z 8 LU ....I· / 7 / ~ / < 6 1- 0 5 1- 4 3 :o:-----_ 2 1 1.0 2.0 ·. 3~0 LENGTH 2nd PER E 0 N ·IT E (m mJ .. · l: ~---- ~ Figure 2. ! Caprellid relative abundance (individuals/linear !. meter of Zostera marina) by month: Vertical line represents the 95% confidence limits for the means, •nd the solid line connects the means. li__ F=------E------Ft: co CJ) .:I: ~ z ·- 0 ·- :E ------ ~=--~-- ------,... ,... ,... ~------ ~3J.3W /SOI113~d\f~ f--0 ~-~ ~ ~~~~~ c ~ ~------rJ p R ~- ---- p -- --~--=-~---=~--=- 6 I' Figure 3. l: ,' Caprellid sex ratio, by month. Vertical lines I represent'the 95% confidence limits for the means and the longitudinal lines represent the mean percents. ~--- :1 ------ ,... ______ --~----- % arcsme~ . . 100 90 .• 97 80 88 70 z o· '75 60 a-· <1: . ...J :::> ·. a. 59 50 . f 0a. .. z 41 40" . t d::; ii ~"=-==':; en t . t:; __ UJ_. 25 30 -- -=-- <( ~ :E 12 20 3 10 .. j j j MONTHS· ·...... t~ [ ______ R~ ------h F6-~-:~:-== i' Figure 4. f--; I! Distribution of males in size classes summed for the entire year. Fifteen size classes with an interval of 0.4 mm., from 0.4 to 6.3. ------ r~----- i;=== ,----~- :::::: ------=- ~------~ ,_. _____~- ~~----~------ •y . % arcsme~ - 100 90 .. . , .. . 97 80 .. ...-- r-- . li 88 70 a------r--- r;---- . ~------z ll 0 - li 75 60 . . 1- __,<( :::> 59 50 a. r-- 0 a.. z 41 40 )H ---- U) .-- w .--- _, 25 30 / <( '• ~ ~ 12 20 :-- 3 10 ~------. I •· 2 3 4 5 6 . 7 8 . 9 10 11 12 13 14 SIZE CLASS ---~ : ~ ~ -~ r: F.==--==::::-:------ - ~c-~-,-- Figure 5. Percentage of female caprellids bearing embryos, by month._Circles represent means; solid circles represent total female population and open circles represent percent adult females. Vertical lines indicate 95% confidence limits for the means. ~-=---=---- -=-__ ::: ~- -- ----- ~ ~- --- '-'~--- p i . ---··------.. ~ !; FI-~ -~-=-__:_~=~-___-~---=::____- ts=::::== % arcsme 'fP - F.------~------ H "100 90 97 80 ,_,__ 8--- -_-_ p :___ ::__::_::__-__~ 88 70 ~ ~ ------ 75 60 CJ) w 59 50 ...J <( :E , . UJ 41 40 u.. ~~'-'-~ 0 ~~--- ~. 25 30 a:· ~ ~. 12 20 3 10 I I ;.; -- I tl [' ______--- a an j j a ·s. 0 MONTHS- ~ ..· ~--- ·- -- -- = ------~·- ~ ------ A R---- ~------Figure 6. g In I' Regression line showing the relationship between i the length of the second pereonite and the number of eggs earried by gravid female caprellids. Regression equation: Y=57.47x - 65.69 • ~- [:____t=====:==::::=:: ------ ~- ' ;__: __ -- -- ~------~- l.~~~ f~ --~-~'~-- . P------90 ~~.,~ ~ - ~ - 80 §·-=-~ ~ .. ~- - ~-----=---= 6 :..___; -----_ _:____ --~ 70 60 '--- ~~- ~ -- --- >-: 0 R I (/') 50 ! G - G UJ 40 ~-.! r. ___::_:____:_:_=---===-=-=--= H p--" -----~--:_- 1 0 • ~------ ------ 1. 0 2.0 3.0 LENGTH 2"~ PEREONITE (mmJ ~-- F " ------'"[='; ~-~----- r1 r. -- 8 ~~-~---~~ F1 n--"------g- -- -- Figure ?. ~- r1,, I ~ Average number o! eggs carried by females o! various i sizes, da~a !rom all months. The center horizontal line represents the mean, the terminal lines the range and the vertical bars the standard error. 6_ ------ E~:--~ ~ ~~~~= ~----~- -- ~---=------90 80 70 60 en so (!) (!) UJ 40 u. 0 a: 3 0 UJ b_-- -- OJ ~~-~----~-- :E ~~~=-~=c ::::> ----- z 20 1 0 '"""'------~----- 2 3 4 5 6 7 !- SIZE CLASS 1 l-~ E ~~~ ~~ . ~--- H r. t:J-~- ,,- -- ~ h -- ~------IJ !::::::;--- --·------·- Figure 8. [J -- --·- .. ~ --=~·- ~~-~~~ Recruitment and number or pre-reproductive females, I' by month. Vertical lines represent 95% confidence limits of the mean, and the longitudinal lines represent the mean percent of juveniles present in the population. Solid line indicates the mean per cent of pre-reproductive females found per month. ~-= ~-- -~~~~===-~ .~------.J ~-----==== =- - --· -· ~----~-- F------·--· ~ -~· --·· ~~~ l'e· % arcsmeff ~--· ~ --·- .. t1 100 90 . 97 80 ~-·-·------~ 88 70 rF~:-.:::-.:__- ~~-~ ~ z R-=--_:__:=------o· . r' ..... 75 GO f m a m J . J a s· 0 n· d J MONTHS· -· . . l ' E'--~---- :·_ --oi--- ·~ - ~ te- Figure 9. t iI Size-frequency histograms in size classes, by month; ~ I ~ a) males, b) females. Represented are fifteen size classes with an interval of 0.4 mm. from 0.4 to 6.3mm. ~=- cc-=c---- g__ _ ~------ = ------t~ 90 90 90 JUNE - 80 FEB 80 APRIL 80 - 70 70 70 ~~c 60 80 60 ... , z 50 .. ..z 50 z 50 Ul Ul Ul 0 0 0 a: 40 a: 40 a: 40 Ul Ul Ul 'A. Q. 30 Q. 30 30 20 20 20 10 10 10 2 3 4 5 6 7 8 9 10 11 12 13 14 2 3 4 5 6 7 8 9 10 11 12 13 14 2 3 4 5 6 7 8 9 10 11 12 13 14 SIZE CLASS SIZE CLASS ~IZE CLAS_S ------ 9"0 90 90 SEPT 80 AUG 80 80 OCT 70 70 70 60 .. 60 60 ..z so z 50 ..z 50 Ul Ul w 0 0 0 a: 40 a: 40 a: 40 lJJ Ul w c. 30 Q. 30 Q. 30 20 20 20 10 10 10 --.--.---< 2 3 4 5 6 8 9 10 11 12 13 14 2 3 4· 5 6 7 8 9 10 1112 13 H 2 3 4 5 6 7 8 9 10 11 12 13 14 SIZE CLASS SIZE CLASS SIZE CLASS 90 90 90 NOV 80 80 DEC 80 JAN 70 70 70 60 ... 60 ... 60 z 50 z 50 1- Ul z 50 0 0 a: 40 "'a: 40 "'0 40 Ul w a: Q. 0. 30 30 "'... 30 20 20 20 10 10 10 2 3 4 5 6 7 8 9 10 11 12 13 14 2 3 4 5 6 7 8 9 10 11 12 13 14 2 3 4 5 6 7 8 9 10 11 12 13 14 CLASS SIZE SIZE CLASS SIZE CLASS ~----- 9a '' ------ r<--~------c-b_~ ------ 90 90 90 80 FEB 80 APRil. 80 JUNE 70 70 70 60 60 60 1- 1- 1- z 50 z 50 z 50 F1 Ul Ul Ul H 0 0 0 0: 40 0: 40 0: 40 Ul Ul w ... 30 ... 30 0.. 30 20 :·r 20 20 1.\. ------10 -'f 10 10 2 3 4 5 6 7 8 9 10 11 12 13 14 2 3 4 5 6 7 8 9 10 1112 13 14 2 3 4 5 6 7 8 9 10 1112 13 14 ---··-- SIZE CLASS ...SIZE .C.LA$5 SIZE_ C!-A.,~!'I.• 8--"' R·------ ~- 9o- · · I· 90 \ ~ 80 AUG 80 SEPT 80 OCT 70 70 70 60 60 60 1- 1- 1- z 50 z 50 z 50 Ul Ul ~- Ul ,o 0 0 0: 40 0: 40 0: 40 Ul Ul Ul 0.. 30 ... 30 a. 30 20 20 10 10 ~----- 2 3 4 5 6 7 8 9 10 11 12 13 14 2 3 4 5 6 7 8 9 10 11 12 13 14 2 3 4 5 6 7 8 9 10 11 12 13 14: F SIZE CLAS!: SIZE CLASS SIZE. .CLASS 'H----- g, " ~--- / ~------~- I. 90 90 90 80 NOV 80 DEC 80 JAN 70 70 70 60 60 60 1- z so ~ 50 1- w w z so 0 Ul 0 0 0: 40 '0: 40 40 w w 0: ... a. Ul 30 30 a. 30 20 20 ~ 20 ~ 10 10 10 i F 2 3 4 7 9 10 11 12 13 14 5 6 8 2 3 4 5 6 7 8 9 10 11 12 13 14 2 3 4 5 6 7 8 9 10 11 12 13 14 i .. ·· SIZE CLASS -- .. I SIZE CLASS SIZE CJASS I 9b F. ;.,------~ ··- '" ______r. __ ------~~- ~~~~-~--- - c ------ R -- ~----- ~ -~ ~~~ ~::=:-~ n------Figure 10. ~ ~--~~ r:: li Percent distribution of male and female caprellids [' in size classes, by month and summed for the entire sampling period. Vertical lines represent the 95% confidence limits and the longitudinal lines reP resent the mean percent distribution of months. The solid line indicates the percent distribution for ~~~-_----::- the entire year summed. F: ~ ·-- -· -· --. --. u ~ ~ ---- - ~------ E c:~~- .... ------;-; . ------~·------~------.. [-' E--~- - ' % arcsme\n> § -___ ·__ c= ~ 40 ~-- r.: 30 20 1 0 40 (/) w "'?- - ..J 30 >=:-----= <( §-- ~ r:------===--~ w ~------~ u. "20 \....: __ _ u. 0 ~ - 10 -1 2 3 4 5 6 . 7 8 . '9 10 11 1 2 13 14 SIZE CLASS --· i - -_ ---•- ;-, l----,--~ -~-~~ ~ -=-·-- ..;- li---- h H Figure 11. Average caprellid size, by month, using length of the second pereonite. Vertical lines represent the 95% confidence limits. 8--- ~- --~~~~=-~"-- ~-=------=------~~==== ~- ~- rF.--- -~-~---~---- >-"------MALE .... 4 . 3 I -'E ,_E I r I 2 I UJ I I 1- ,_, -z 6----- 1 p - .. - 0 ~ _-·- - ~=·"------UJ F--' a: [: ·w I a. "0 FEMALE c: 4 ('~ .. J:, ·3 == ---- - 1-: p-~=------=-=-==--=- (!) . ~------<=-!------=-=------=----= c---- z r:~~~- I I ~ 2' I ~c_:cc.C:.-c=~=cc·=_ I ~------~- I I 1 1 ~-- . . . I • ! I I • . f m a m j . J a ·s- 0 n· Ci j J978 1979 M9NTHS· -· ----- c..:i ______ F'- Figure 12. Final orientation of individuals following agonistic interaction. a) male vs. female combat: solid line. male winner; dotted line. female winner; alter nating line. total summed combats. b) male vs. male combat: solid line. aggressor ,wins; dotted line. larger male wins; alter•· g---- nating line. total summed combats. "E----=-=-----_------:::-,. M== ~------ f. r· ,. ------_;·_: tir' -- ~o. arcsme \[0 41 40 r.---~ ...-. - I ci . ~--· -- / l'.\ 25 30 ;·lj 1 12 20 I I I I w -----~---- 3 10 I I .. I I· I 41 40 i I 25 30 I I: . . . \~ /;/ p----=-==-=-=-==--=~·-... -.~- 12 20 \ • I \~\ I I I \ "II I \ II'// I .\·,\ I I 3 10 \ ·.:./I .. \ I \ I \ / \ I FACING EACH BOTH TURNED LOSER FACING WINNER FACING OTHER AWAY WINNER LOSER .. OUTCOMES .·. ~ .. · ~-.--' Table 1 !" ____ Chi square test for goodness of fit for sex ratio. SEXES OBSERVED EXPECTED DEVIATIONS DEVIATIONS 2 8------ FREQ. FREQ. SQUARED if-Q fi t f r-? Male 1398 1617.5 -219.5 48180.25 29.79 Female 182Z 161Z.5 212!2 48180.25 221Z2 ------~ ~---.- 3235 3~~35 0 58.58*** 1---'------h--~ ------ii fi *** P< 0.005 ~-- F=----=-===------==-= =----=-o-----=-=-= ----=-=--- ~-. ·-·--··--·---··· .. 'table 2 Three-way analysis of variance of size distribution measured for both sexes eight times over the course of twelve months •• ~-- -- H Degrees of Sums of Mean Source freedom squares square F-ratio A Size claall 13 20740.6305 1595.4331 33.084*** B Months l~ 8 129.8138 16.2267 .336 ns ~ ;._;_ ----- g - f---- - C Sex r: 1 669.0499 669.0499 13.874*** \ ~ AB ~ 104 12910.1719 124.1363 2.574*** AC 13 3498.6781 269.1291 5.581*** BC 8 15.7769 1.9721 .041 ns ABC 104 5015.3224 48.2243 Total 251 .!.:42979 ~442 R.------, F.001 (1,60)= 1~.0 F.001 (12,~0)= 3.31 F.OOl (60,60)= 2.25 " ~-- - ***·=P(O.OOl F---= --~~~------~~----~~~-- --~ Table 3 Single classification analysis of variance of vertical position of males and females. f+----~ t] Degrees of Sums of Mean Source freedom squares square F-ratio Sexes 1 2205.8 2205.8 27.65*** Error 202 16116.06 79.78 ~ r::.: F§ Total 203 18321.86 ""~--- -- h------!;h F.001 (1,120)= 11.4 *** =P :o--;------"04 -- --- b --- =-----=-----o~-=-=- -~---~ Table ~-- 4 >-~ t::-~- ___--- -- . ·- -·--_ Two~way analysis of variance of vertical position of males and females on four different substrate treatments. b-;-- ~--- Degrees of Sums of Mean Source freedom squares square F-ratio A Treatments 3 79.1615 26.3872 .3985 ns B Sexes 1 4226.88 4226.88 63.833*** . AB Error ...2.... 84.2615 28.0872 .4242 ns Total 7 4390.303 F.OOl (1,120)= 11.4 *** P(().001 ~------11 ~J ~--- •.. .. " ~~== ·~ ·I ~---=-- --~------~------ ..._ -- -~------Table 5 ~-~ Three-way contingency table testing the independence of size, aggressive behavior and combat success in male Vp. male interactions. p ___ ---- Hypothesis Tested Degrees of Freedom G Size X Aggression Independence 1 .06 ns Size X Success Independence 1 6.64** q - Aggression X Success Independence 11.1*** "'-E - H ~ Size X Aggression X Success Interaction 1 2.84 ns [' i 4 20.64*** *** P<0.005 ** P Data Raw ~ -- ;-···/ ·.Asgz:e,ssion Success won lost_.. __ Aggressive 22 5 Large Not Aggressive 16 7 Aggressive 21 7 Not Large Not Aggressive 7 ~ ' _:·. 19 ;!-·------Table 6 ; -- - - Movements of combat loser following interaction. - - - - - ~...... ____ _ ~ ~== l-~ Movements Male vs. Male Female vs. Male Loser driven off 46.5% 45.3% Loser not driven off 53.5% 54.7% Aggressor wins loser stays 47.7% 66.7% Receiver wins loser stays 44.4% 42.3% Large aggressor wins loser stays 44.4% 66.7% Large receiver wins loser stays 42.8% Combat a draw both stay 100.0% 100.0% f, ~ f~~==== ~~~---o--~~=- nr------r' =-----=-----__-_ - E----§____ _ ~--. ------