Phenology
Ceratina nigrolabiata excavate new nests mainly in May and June, however, some newly excavated nests were also recorded later in the season (Figs. 1, 2). Active brood nests (Table 1) occurred from half of June and appeared in high proportion through whole July. First full brood nests first occurred at the end of June, but the main peak of full brood nests was in July. Full brood nests were also frequent in August. Full-mature and mature brood nests occurred from the end of July, and they were very frequent through August. Other types of nests occurred mainly in the beginning and at the end of season. At the beginning of the season occurred mainly old hibernacula or adults of C. nigrolabiata visiting nests of other Ceratina. In the late phases of season occurred abandoned nests with only parasites and newly excavated burrows for hibernation.
Nesting cycle of C. nigrolabiata. (a) newly excavated nests—burrow which contains only adult(s) and sometimes fillings. (b) discarded nest—burrow where previous nest was discarded, and there are pollen remnants on the walls (c) active brood nest—nest in phase brood cell provisioning (d) large active brood nest, where egg is present at the top, but young adults already developed at the bottom of nest (f) guarded full brood nest—mother guards this nest (f) plugged full brood nest—nest is unguarded and closed by a thick filling plug (g) orphaned full brood nest—last brood cell partition is thin and above it is commonly pollen from incompletely provisioned brood cell (h) full-mature brood nest—this nest contains juveniles, young adults, and sometimes mother (i) mature brood nest—this nest contains young adults and sometimes mother. All these figures are hypothetical examples, they are not based on concrete dissected nests.
Phenology of C. nigrolabiata through nesting season.
Type of nest founding
We found two types of newly founded nests. Newly excavated nests, which were built by excavating pith from a twig. Discarded nests are the other type. These nests were built from previous nest of Ceratina (probably other C. nigrolabiata in most cases) by discarding a part of or all original offspring (Figs. S1 and S2). We observed nests of C. nigrolabiata, where nest partitions were destroyed and pollen from brood cells was placed on side of the nest. We suppose that original offspring were discarded out of the nest (and on several occasions, we observed discarding of offspring out of the nest). Pollen provisions of the previous nest owner were usually moved to the sides of the nest (Fig. S1). From newly founded nests, 82.69% (86/104) were newly excavated and 17.30% (18/104) were discarded nests. When we counted only nests founded after half of June, the proportion of discarded nests was 22.78% (18/79). From active brood nests, 4.66% (29/622) had apparent relics of usurpation and discarding.
Presence of parents
Newly excavated nests
In newly founded nests, only male was present in 53.48% of nests (46/86, Table 2), only female was present in 10.46% of nests (9/86) and male and female together were present in 36.04% (31/86) nests. Newly founded nests were on average 5.47 cm long (SD = 4.68, range 1–22.1, N = 86). Nests with only male were on average 3.82 cm long (SD = 3.26, range 1.2–16.7, N = 46), nests with only female were on average 5.73 cm long (SD = 4.72, range 1–14.1, N = 9), nests with both male and female were on average 7.85 cm long (SD = 5.49, range 1.9–22.1, N = 31). Nests with both parents were significantly longer than nests with only a male (Tukey HSD test on logarithmic data, difference = 0.6743, p = 0.0003), but not significantly longer than nests with only a female (Tukey HSD test on logarithmic data, difference 0.4427 p = 0.2256).
Discarded nests
In 72.22% (13/18) of discarded nests one male and one female were present. Female and two males were present in two nests, only a male was present in one nest, only a female was present in one nest and no adult was found in one nest.
Active brood nests
We found male–female pair in 84.72% of nests (527/622), female and two males were found in 1.29% of nests (8/622), female and three males were found in 0.16% (1/622) of nests, no adult was present in 1.76% (11/622) of nests, only male was in 5.6% (35/622) and only female in 6.43% (40/622) of nests.
Full brood nests
Most of full brood nests (73.51%, 493/672) were not guarded by any parent (Table 2). When a full brood nest was guarded, then usually by a female (15.18%, 102/672). Only male was present in 4.31% (29/672) and male and female were present in 7.14% (48/672). Males were significantly more often present in nests, where female was also present, than in nests without a female (Chi-square test, Chi = 81.06, df = 1, p < 2.2e−16).
Full-mature brood nests
Most of full-mature brood nests were not guarded by any adult of parental generation. No parent was present in 57.67% of nests (102/177). If guarding adult was present, it was usually a female in 27.11% (48/177). A pair of male and female was present in 10.73% (19/177) and only male was present in 4.51% (8/177). Interestingly, an old female was present more often in full-mature brood nests than in full brood nests (Chi-square test, Chi = 16.96, df = 1, p = 3.826e−05).
Mature brood nests
Usually, a nest was not guarded by any adult of parental generation (80%, 68/85). Nests guarded only by male and only by female were present in the same proportion 9.51% (8/85). In one case a nest guarded by male and female together was present.
Duration of actual male presence
The male found at the time of nest dissection remained in the active brood nest for 10.77 days on average (N = 302, SD = 7.52, range 1–38). In full brood nests, the male found at the time of nest dissection remained there for 4.93 days on average (N = 30, SD = 6.73, range 1–25). However, the difference between nests with male and female couple and nests where a male was present alone was significant (quasipoisson GLM with year and duration of nest observation as covariable, df = 1 and 23 p = 4.609e−06, deviance = 67.636, residual deviance = 77.051). Males remained for 7.55 days on average (SD = 7.68, N = 18, range 1–25) in nests, where female was also present, but only 1 day on average (N = 12, SD = 0) in nests where only male was present. In full-mature brood nests, male stayed 3.33 days on average (N = 6, SD = 2.5, range 1–8) at the time of nest dissection. Sample size is too small for testing the difference between nests where a female was present and absent, but we observed both males which stayed in a nest one day and males which stayed multiple days.
Paternity of nests with small number of offspring
Guarding male was usually not the father of offspring in young provisioned nests. Guarding male was the father of 6.25% (10/160) of all offspring and 9.9% (10/101) of female offspring in nests with 1–3 offspring (N = 70 nests). No offspring was fathered by guarding male in nests with only one offspring (N = 17). The proportion of offspring guarded by it´s own father was 6.2% (2/32) in nests with two offspring and 7.2% (8/111) in nests with three offspring.
Structure of full brood nest
Full brood nests contained on average 7.59 brood cells (range 1–21, SD = 3.76, N = 566). Empty cells were relatively scarce, but usually present. There were 1.33 (range 0–8, SD = 1.33, N = 530) empty cells per nest on average. Therefore, brood cells were usually adjacent. However, when an empty cell was present, it was usually much longer than a brood cell (Fig. 3). Length of nest was 15.12 cm (N = 670, SD = 4.08) on average and entrance burrow was 3.63 cm long (N = 657, SD = 3.63) on average.
Examples of nests structure of full brood nests of C. nigrolabiata. Pictures of all nests are based on real dissected nests.
We distinguished three types of full brood nests: (1) guarded nests, (2) plugged nests, (3) orphaned nests. In guarded nests, an old female was present. The Last brood cell was always closed by nest partition. Other two nest types, plugged or orphaned nests, were without presence of an old female. Plugged nests had the last brood cell closed by a filling plug. Filling plug was much thicker than the regular nest partition (Fig. 3) Filling plug was 1.41 cm long (N = 307, SD = 0.87, range 0.2–8.0) on average. Moreover, plugged nests had usually modified nest entrance. All pith between nest entrance and a filling plug was excavated. In orphaned nests, the last brood cell was closed by a regular partition, which was not thicker than regular brood cell partition. Sometimes, the last brood cell was partially provisioned by pollen and was not closed by brood cell partition. This type of brood cell did not contain living offspring.
Comparison between different full brood nest strategies
The most common type of full brood nest was plugged full brood nest (53.42%, 359/672). The proportion of orphaned (24.25%, 163/672) and guarded (22.32%, 150/672) nests was similar. The number of brood cells was 9.85 on average in guarded nests (SD = 4.14), 6.68 (SD = 3.53) for orphaned nests and 7.06 (SD = 3.30) for plugged nests (Table 3). Number of brood cells was significantly affected by year (Anova, df = 5 and 558, F = 24.418, p < 2.2e−16) and also different between nest types (Anova, df = 2 and 558, F = 27.265, p = 5.039e−12). However, post hoc tests show that guarded nests are different from plugged (Tukey HSD test, p = 0.0000) and orphaned nests (Tukey HSD test, p = 0.0000), but there is no difference between plugged and orphaned nest (Tukey HSD test, p = 0.1460). Length of nest significantly differed between years (Anova, df = 5 and 659, F = 3.8134, p = 0.002059), but did not significantly differ between nest types (Anova, df = 2 and 659, F = 0.4224, p = 0.655643). Length of nest entrance significantly differed between years (Anova, df = 5 and 638, F = 7.1525 , p = 1.592e−06), and also in full brood nests (Anova, df = 2 and 638, F = 296.7088 p < 2.2e−16). Tukey HSD tests showed significant difference between all three nest types. Longest was nest entrance in orphaned nests (mean 7.93 cm, N = 157, SD = 4.67), after it in guarded nests (mean 4.00 cm, N = 148, SD = 3.76) and then the shortest in plugged nests (mean 1.56 cm, N = 352, SD = 1.21, Table 3).
There was a distinct difference in the proportion of full brood nest strategies through the season. The proportion of plugged nests was highest at the beginning of full brood nest season (beginning of July) and later decreased. On the other hand, the proportion of guarded and orphaned full brood nests increased from a beginning of July to August (Fig. 4). The proportion of full brood nest types significantly differed between different periods in season (Chi-square test, Chi = 116.87, df = 10, p < 2.2e−16).
Proportion of types of full brood nests through the season.
Parasites
The most common nest parasites were Ichneumonidae and Gasteruption. Both destroyed multiple brood cells and commonly destroyed a large part of a nest. We found an ichneumonid parasite in 6.81% (125/1836) of nests and Gasteruption in 2.83% (52/1836) of nests. In 38 cases, we were unable to determine if the parasite is an ichneumonid or Gasteruption. When we suppose the same proportion of both parasites in determined and undetermined larvae, we can assume that 8.26% of nests were parasitized by Ichneumonidae and 3.44% by Gasteruption. Usually, there was only one larva of these parasites per one nest. We observed 8 cases of two Ichneumonidae larvae in one nest, 2 cases of two Gasteruption larvae in one nest and 2 nests where Gasteruption and ichneumonid larvae were present together.
Proportions of attacked nests differed between nesting phases. No new founding nests were attacked, as there is no food for the parasite. In active brood nests, only 2.74% were parasitized by Ichneumonidae and only 1.43% by Gasteruption. In full brood nests, 11.68% were parasitized by Ichneumonidae and 4.83% by Gasteruption. The complete number of parasitized nests is summarized in Table 4.
The proportion of nests attacked by ichneumonid or Gasteruption parasites was 16.66% (25/125) for guarded full brood nests, 11.04% (18/163) for orphaned full brood nests and 17.27% (62/359) for full brood plugged nests. Presence of parasite which consumed multiple brood cells (Ichneumonidae or Gasteruption) did not significantly differ between years (Binomial GLM, df = 5 and 666, deviance = 35.95, residual deviance = 566.37, p = 9.717e−07), and also did not differ between full brood nest types (Binomial GLM, df = 2 and 664, deviance = 3.651, residual deviance = 562.72, p = 0.1612). When we excluded nests attacked by an ichneumonid or Gasteruption parasite, the proportion of live brood cells differed significantly between years (Binomial GLM, df = 5 and 559, deviance = 33.034, residual deviance = 1291.1, p = 3.706e−06) and also between full brood nest types (binomial GLM, df = 2 and 557, deviance = 13.252, residual deviance = 1277.8, p = 0.0013255) The proportion of live offspring was 83.41% (N = 127 nests) for guarded nests, 77.92% (N = 141 nests) for orphaned nests and 82.74% (N = 298 nests) for plugged nests.
Other parasites were very rare. We found chalcidoid wasps in 0.44% (8/1836), Malachidae beetles in 0.16% (3/1836) and conopid flies in 0.05% (1/1836) of nests.
Developmental stage diversity in active brood nests
Ceratina nigrolabiata have very fast development in comparison to the rate of provisioning. In 5.14% (32/622) of active brood nests were at least one offspring in the adult stage. Active brood nests, where an adult was present in the innermost brood cell, had a large number of brood cell provisioned (mean 13.71, SD 2.59, range 6–19, N = 29) in comparison to nests, where younger stages were present at the bottom of the nest. Nests with pupa at the bottom had 10.8 brood cells on average (SD-2.84, range 5–19, N = 144). Nests with larva at the bottom had 5.69 brood cells on average (SD = 2.25, range 1–15, N = 268). Nest with egg at the bottom had 2.2 brood cells on average (SD = 1.15, range 1–6, N = 83).
Source: Ecology - nature.com
