CEMENT GLAND DEVELOPMENT, OVARY MATURATION, AND REPRODUCTIVE CYCLES IN THE AMERICAN

LOBSTER HOMARUS AMERICANUS

D. E. Aiken and S. L. Waddy

A B S T R A C T

Four developmental s tages are defined for the cement glands of mature female American lobsters. These " c e m e n t g lands" are tegumental glands that cycle in phase with ovary de-

ve lopment and secrete a subs tance that appears to be involved in the egg fertilization-at- t achment process . Since cement glands do not develop in male or immature female lobsters, they can be used to de termine maturity in females that are not ovigerous.

In wild populat ions, size at maturity is frequently based on sizes of ovigerous females , but

this assessment is compl icated by the exis tence o f two different reproduct ive pat terns in the Adult-I year, the fact that only half of the mature females are ovigerous in any year, and the

fact that ovigerous females often are not adequate ly sampled by traditional trapping proce- dures. Cement gland deve lopment can be used to improve the accuracy of maturity assess- ments by providing information on maturity of barren females.

Max Braun (1875, 1876) was the first to recognize and describe decapod cement glands, but it was Cano ' s comprehensive studies (1891) that were most effective in directing attention to these structures. Two years later Herrick (1893) provided a brief description of cement glands in the pleopods of the American lobster, and this was followed by additional descriptions of the glands in both the American and European lobster (Herrick, 1895, 1909; Yonge, 1932, 1937).

Cement glands and tegumental glands have a similar structure at the light mi- croscope level of resolution, and the former are generally considered to be teg- umental glands that cycle in phase with ovarian development and perform a reproductive rather than a molting function (Herrick, 1895; Yonge, 1932, 1937). Whether the cement and tegumental glands of Homcarus are structurally identical is not known; the ultrastructure of tegumental glands has been examined in Hom- arus (Arsenault et al., 1979), but we know of no comparable study of the cement glands in this species.

Although several hypotheses have been advanced, there is still no conclusive statement concerning the role " c e m e n t " glands play in the process of egg extru- sion, fertilization, and attachment. Braun (1875, 1876) decided they secreted the cement that secures the extruded eggs to the pleopods (hence the name), and the literature contains some lively discussion on the pros and cons of this and other suggested functions. It has been clearly established that there is a good correlation between ovary development and cement gland development in Homarus and other macrurans (Aiken and Waddy, 1980; Cheung, 1964; Herrick, 1893, 1895, 1909; Lowe, 1961; Stephens, 1952; Yonge, 1937). As the oocytes undergo vitel- logenesis, the cement glands become progressively more engorged with an opaque white substance. In crayfish the contents of the cement glands are discharged onto the abdominal s terna immediately before oviposition (Andrews, 1906; Yonge, 1937), and this is assumed to occur in Homarus as well, since the glands become vacuolated during oviposition (Herrick, 1909; Yonge, 1937). However , they have been said to recover after extrusion (Yonge, 1937), an aspect that would be difficult to explain with any of the standard hypotheses of function.

Cement glands are not present on male or immature female Homarus . They begin to develop for the first time in the pubertal female as the previously un-

Table I . Morphological criteria for categories o f ovary deve lopment in H o m a r u s amer icanus (Adapt- ed f rom Aiken and Waddy . 1980).

developed (white) ovary undergoes vitellogenesis. Cement gland development can, therefore, be used in the determination of female maturity in this species. This paper describes a staging method for the degrees of cement gland develop- ment and relates these stages to ovary development and the reproductive cycles of female American lobsters.

METHODS

Cement gland development was correlated with ovary development in 531 females sacrificed at all months of the year, with primary emphasis on the period May-October. Ovary criteria were based on those in Aiken and Waddy (1980), summarized in Table 1. The relationship between cement gland development, maturity, and oviposition was defined by following 296 females in the laboratory for 3 years under local photoperiod and temperature regimes. Additional data were gathered from 50 fe- males obtained from the Gulf of St. Lawrence commercial fishery in early May and held throughout the summer, and from 137 females obtained from the western Northumberland Strait fishery in Oc- tober and held in the laboratory for a year under either ambient or simulated local photoperiod and temperature regimes.

For analysis of cement gland development, pleopod endopodites were either severed with scissors, placed on a microscope slide in a drop of sea water, and photographed with transmitted light on a Wild M400 Photomacroscope, or photographed in .situ with a 55 mm Micro-Nikkor lens and 25 mm M2 extension, using reflected light from an electronic flash. A sequential photographic record was thereby compiled for each female.

RESULTS

Cement Gland Morphology

A tegumental or " c e m e n t " gland consists of a cluster of 30-50 secretory cells, a duct cell, and a central cell (Fig. 1). The secretory cell and the duct cell are arranged in radial fashion around the central cell (Arsenault et al., 1979). This radial arrangement has given rise to the term " rose t t e " (Herrick, 1895; Yonge, 1932, 1937) to describe the appearance of the active gland. When viewed with transmitted light (Fig. 2), the active gland appears more opaque toward the center,

Fig. I. Cement or tegumental glands of H o m a r u s as figured by A, Herr ick ( 1895); B, Yonge (1932); and C, Arsenaul t et nl., (1979). D, representat ion of a Stage 3 cemen t gland as seen in .situ with transmit ted light. The so-called " r o s e t t e " is the dark central region, actually secretory product in the secretory cells. Secre tory cell (sc), central cell (cc), and duct cell (dc) are indicated in C.

Fig. 2. Stage 3 cement glands of H o m a r u s showing " r o s e t t e s " formed by opaque secretory material concen t ra ted toward the cen te r of the gland. cg, cement gland; ch, chromatophore ; r, roset te of secre- tory material.

and it is this opaque region filled with secretory product that is perceived as the " r o s e t t e " (Figs. ld, 2).

Cement glands double in diameter during development from the inactive (Stage 1) to the fully engorged state (Stage 4), with the most dramatic increase occurring between ovulation and oviposition. Measurements were made in gland Stage 3 (mature ovary before ovulation) and in gland Stage 4 (after ovulation). Mean gland and rosette diameter for 12 lobsters with Stage 3 glands was 139 and 93 Am, respectively. For 14 lobsters with Stage 4 glands, mean diameter was 288 and 240 Am. This is considerably larger than the 80 Am reported by Yonge (1937), but comparable to the size suggested by Herr ick 's (1895) drawings.

Cement Gland Stages

Stephens (1952) defined 4 stages of cement gland development in the crayfish Orconectes, and these are adopted here in modified form for Homarus . In Or- conectes, the uropods and telson are used for staging, but in Hornarus the cement glands are most accessible on the pleopods and most abundant on the endopoditc of the pleopod. For this reason the endopodite is preferred for staging, and many of the criteria outlined below apply only to this appendage.

Advanced cement gland development (Stages 3 and 4) is obvious on gross examination with the unaided eye, but early development (Stages 1 and 2) is difficult for the inexperienced observer to detect, and questionable pleopods should therefore be examined microscopically with transmitted light. Pleopods clipped from the lobster for subsequent staging can be stored in cold sea water ( - 2 ' C ) for more than 24 hrs without loss of gland integrity.

Fig. 3. A, regions of the pleopod endopodite useful for staging cement glands of Homarus. B, left third pleopod showing segments and groups of nonplumose setae (from Herrick, 1909). b, basipodite; c, coxopodite; en, endopodite; ex, exopodite; nps, nonplumose setae, groups 1-7.

For staging purposes the pleopod endopodite is considered to have an anter ior and a posterior face, a proximal and a distal end, and a medial and a lateral edge (Fig. 3). The medial and lateral edges each occupy one-third of the endopodite width. On the endopodite of the third pleopod the division between proximal and distal is close to the lower limit of nonplumose setal group #5 . All divisions are approximate and are intended only as guidelines. In general, cement gland activity starts along the medial and lateral edges of the endopodite (more rapidly in the medial), progresses into the central region (primarily the proximal end), and fi- nally develops in the distal end. This progression of development is utilized in the following staging criteria and illustrated in Fig. 4.

Stage 1 . - T i s s u e thickened between nodes along lateral and medial edges, but

Fig. 4. Cement gland of Homarus stages 1-4 illustrated with whole mounts of pleopod endopodites (upper) and enlarged view of lateral or media] region (lower) showing individual cement glands (cg).

individual glands not visible to unaided eye. With transmitted light at x 10 and x 20, individual glands oaf -100 홢m may be seen as small indistinct spots, but no " ro se t t e s " are formed.

Stage 2 . - S o m e cement gland activity apparent in central region, especially proximal end. Some glands with rosette appearance when viewed with transmit- ted light at x10 to x20. Visible to unaided eye as small white dots medial to nodes.

Stage 3 . - G l a n d rosettes well developed in central region of endopodite. Visible to unaided eye as distinct white dots in central region and continuous white mass in medial and lateral regions. Glands 100-150 ¡Lm diameter. Ratio of rosette to gland diameter less than 0.75.

Stage 4 . - G l a n d s engorged throughout, often appearing to be arranged in rows. Visible to unaided eye as a continuous white mass in lateral and medial regions and in proximal portion of central region. Diameter of glands greater than 200 tLm; ratio of rosette to gland diameter greater than 0.75.

Degenerating (Fig. 5 ) . - V a r i a b l e number of large cement glands scattered throughout pleopod, but general cement gland development more typically Stage 1. Condition associated with resorbing or spent ovaries.

As noted by Stephens (1952), many glands are not clearly one stage or the other, and intermediate stages (i.e., 3.5) can be assigned. As yet there is no evidence of a physiological basis for this distinction.

Fig. 5. Degenerative cement gland condition in Homarus that develops after extrusion or when a ma- ture ovary is resorbed. A, pleopod endopodite viewed with transmitted light. B, same with reflected light. Degenerated cement glands can be seen as flecks in the central region of the pleopod. In C, these degenerated glands (cg') are shown with Stage I glands (cg). D, enlarged view of degenerated cement glands.

Table 2. Representa t ive molt and reproduct ive cycles, ovary categories, cemen t gland stages, and abdomen width indices for female lobsters f rom the Gulf of St. Lawrence during spring and summer.

Correlation with Ovary Development

Cement gland stages were correlated with ovary development in females sac- rificed at all months of the year, with primary emphasis on the period M a y - October. Results are summarized in Table 2.

The ovary in immature females is small, uniformly white, and classified Cate- gory 1 (Table 2). There is no cement gland development associated with this category. In the prepubertal year the oocytes undergo primary vitellogenesis and their color changes progressively from white through yellow to pale green (ovary Category 2), reaching medium or dark green (ovary Category 3 or 4) by October. Cement glands develop to Stage 1 during the prepubertal year but do not progress further.

The criteria for a Category 4 ovary are broad. The ovary factor may vary from 120-325, and the oocytes may range from 0.1-1.6 mm diameter. This is the cat- egory in which most mature ovaries overwinter. As a general rule, the ovaries of pubertal females, ovigerous females, and females from which larvae have been hatched will have reached Category 4 (i.e., dark green with some oocytes larger than 1.0 mm diameter) by autumn. Most of these ovaries will be relatively light in weight (ovary factors less than 200) because they contain a significant propor- tion of undeveloped oocytes and a wide range of oocyte sizes (Fig. 6). Vitello- genesis and oocyte growth continue through the autumn, and by midwinter most

Fig. 6. Range of oocyte development of Homaras in a Category 4 ovary in late summer-autumn.

oocytes in the Category 4 ovary will be 0.8-1.6 mm diameter and the ovary factors will be greater than 200.

Ovary Category 4 is associated with the full range of cement gland development (gland Stages 1-4, depending on season and reproductive state). Table 2 indicates the cement gland stages to be expected each month during the Adult-1, -II, and -III years. Cement gland samples during May are not very revealing, but samples from June through September, in combination with other maturity criteria, will indicate most of the mature females in the population. (Where months and seasons are indicated, they are for Gulf of St. Lawrence lobsters. Appropriate adjustments must be made for other localities according to local reproductive patterns.)

D I S C U S S I O N

In the literature, cement glands have also been referred to as tegumental glands, pleopodal glands, and abdominal glands. Tegurnental g land is not a satisfactory term because it does not differentiate between the glands that cycle in relation to molting and those whose activity is associated with ovarian development. P leopndal g land (Burkenroad, 1947) is anatomically descriptive but ignores the

fact that heavy concentrations of the glands are also found on the uropods, telson, and abdominal pleura of some species. Abdominal g land (Aiken and Waddy, 1980) avoids that criticism but is not very descriptive. The term cement g land originated with Braun (1875, 1876) and is probably a misnomer, since contem- porary opinion holds that the secretion from these glands is not the cement for egg attachment. Nevertheless , cement gland, like " Y organ," is a generally rec- ognized term with historical significance, and for this reason it is the term used in this paper.

Cement Gland Function

Surprisingly little can be said regarding the function of cement glands or the mechanisms that control them. Lloyd and Yonge (1940) considered cement gland activity to be controlled by an ovarian hormone, but Stephens ' experiments (1952) suggested that both the ovary and the cement glands are controlled by an eyestalk factor.

As to the function of the cement glands, the literature discussion has been protracted and perplexing. Braun (1875, 1876) assumed that the secretion from the glands was the cement that secured the extruded eggs to the pleopods. Herrick (1893) and others accepted this, although Herrick had some perceptive reservations. Cement gland function, therefore, became an integral part of the egg membrane- egg at tachment conundrum. Yonge (1937) appeared to settle the question of egg membrane formation and egg at tachment when he provided histochemical evi- dence that the secretion from the cement glands and the outer membrane and funiculus of the at tached egg were identical. However , Cheung (1966) found they were not identical. Even more remarkable, he found that the outer membrane was not the last to be secreted, as Yonge's work suggested, but the first. The outer membrane of the egg (and presumably the funiculus) appear to be derived from the "vi tel l ine" membrane, a two-layered membrane secreted by the oocyte while still in the ovary (see Brown, 1966; Hinsch, 1971). Rather than relying on an external source of cement, the egg appears to secrete its own adhesive sub- stance. It also appears to secrete all of the 4 or 5 membranes found on the at tached egg. What then of the mucoid secretion from the "cemen t glands"?

Burkenroad (1947) suggested that the mucoid secretion from the cement glands is an enzyme-like substance that is necessary for a t tachment of the eggs. Dennell (1947), and Stevenson and Schneider (1962), found that the glands formed tyro- sinase which could be used for phenolic hardening of the egg membranes. Cheung (1966) considered these possibilities, but preferred the view that cement gland secretion provides a favorable medium for external fertilization in macrurans. Cheung's hypothesis is supported by the fact that unfertilized eggs do not at tach well in Homarus (Aiken and Waddy, 1980). Some are lost immediately; others may attach precariously and be lost over succeeding weeks. This suggests that good egg at tachment depends on an interaction between sperm, egg, and cement gland secretion.

Yonge (1937) deepened the mystery with his statement that ducts from the cement glands of Homarus aggregate in bundles that run into the bases of the nonplumose setae and (presumably) discharge along the sides of these setae. This implies a limited secretion by the cement glands, since a substantial effusion would cover plumose as well as nonplumose setae. And yet Herrick referred to the "abundan t milky or turbid secretion from these glands." Furthermore, it can be seen in Fig. 4 that a significant proportion of the cement glands on the pleopod endopodite are remote from the nearest bundle of nonplumose setae, and that a

considerable network of ducts would be required to transport secretion from the glands at the distal end of the endopodite to the nearest nonplumose seta at the proximal end of the endopodite. Clearly, there is more to be learned about even this aspect of cement gland function.

Cement Glands and Reproductive Cycles

Female Homarus are classified as pubertal the year before their first egg ex- trusion, and Adult-I in the season they first extrude eggs. The Adult-I reproduc- tive class is unusual in that ecdysis and egg extrusion may occur in the same summer. This results in two different reproductive patterns, designated Adult-la and Adult-lb. The former is the " n o r m a l " situation in which ecdysis and ovi- position occur in alternate years. Adult-Ib is an alternate pattern in which both ecdysis and oviposition occur in the same summer. Cement gland development is also different in the two groups. The glands become engorged during spring in Adult-la, but in Adult-Ib females they remain undeveloped until after the summer molt.

Information on the prevalence of the lb reproductive class in wild American lobsters is limited but suggestive. Ennis (1980) found that nearly 18% of female Newfoundland lobsters examined be tween 1975 and 1978 had molted and spawned in the same summer. Since these tended to be at the low end of the size distribution, Ennis suggested they were spawning for the first time (i.e., Adult-I year). Robinson's (1979) information from Gulf of St. Lawrence tag returns in- dicated approximately 19% of ovigerous females (predominantly Adult-1) had molted and then spawned in the same summer. In our laboratory studies approx- imately 19% of Gulf of St. Lawrence Adult-1 females have molted and spawned in the same summer, but this phenomenon occurred in less than 1% of subsequent adult reproductive classes. Therefore, the available field and laboratory data sug- gest that 15-20% of Adult-I females from the Gulf of St. Lawrence may molt and spawn in the same summer.

Less information is available on lobsters outside the Gulf of St. Lawrence. Robinson's (1979) data indicated fewer than 1% of females from Atlantic waters off the coast of Nova Scotia molted and spawned in the same summer. Molting incidence is clearly affected by temperature, and summer water temperatures along the exposed Atlantic coast are considerably lower than those in many areas of the Gulf. Ennis (1980) found that the incidence of new-shelled ovigerous fe- males varied according to locality and year, which is consistent with a temper- ature effect. If this proves to be the case, we could expect the Ib reproductive class to be more common in areas such as the Gulf of St. Lawrence and western

Long Island Sound that have relatively high summer water temperatures, and virtually nonexistent in areas such as the Bay of Fundy.

Size-at-maturity is traditionally estimated from the sizes of ovigerous females in the population. This method assumes that the sizes and relative numbers of ovigerous females in the population are well represented in the samples obtained for analysis. Unfortunately, this is seldom the case, although the reasons for this are not clear (see Ennis, 1980, for discussion). It is therefore desirable to enhance maturity determinations by including criteria other than presence or absence of eggs. Several are available (Aiken and Waddy, 1980), but cement gland devel- opment offers the best combination of speed, reliability, and ease of application. Robinson (1979) employed an earlier version of this cement gland staging tech- nique in field samples. He considered that a female had "expressed maturi ty" if she had either extruded eggs or demonstrated cement gland development indic-

ative of extrusion. This approach increases the reliability of field maturity as- sessments, but the existence of the Adult-lb reproductive class introduces a com- plication the field biologist must be aware of. Barren mature females other than Ib would normally have well-developed cement glands by June-July. However , class Ib females retain their undeveloped Stage 1 cement glands until after the summer molt (July-August) and will, as a result, appear to be in their pubertal year if sampled in spring or early summer. In the Gulf of St. Lawrence, and possibly other areas with high summer water temperatures, this could result in a significant sampling error. Therefore, the timing of field maturity assessments is very important unless the stock being studied has a very low incidence of the Adult-Ib reproductive class.

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RECEIVED: 7 April 1981. ACCEPTED: 21 April 1982.

Address: Fisheries and Environmental Sciences, Department of Fisheries and Oceans, Biological Station, St. Andrews, New Brunswick EOG 2X0, Canada.