Investigating the role of non-helpers in group living thrips
Data files
Aug 20, 2024 version files 60.90 KB
Abstract
Behavioural variation among individuals is a hallmark of cooperative societies, which commonly contain breeders and non-breeders, helpers and non-helpers. In some cases, labour is divided, with non-breeders “helping”. Conversely, in some societies, subordinate non-breeders may not help. These individuals may be (i) an insurance workforce ensuring continuity of help for breeders when other helpers are lost, (ii) conserving energy while waiting to breed themselves, or (iii) simply of too poor physiological quality either to help or breed. In the Australian Outback, Acacia thrips Dunatothrips aneurae (Thysanoptera) glue Acacia phyllodes into “domiciles” using silk-like secretions, either alone or cooperatively. Domicile maintenance is important for humidity, so repair can be interpreted as helping. I found that not all females helped to repair damage; some repaired partially or not at all ("non-helpers"). At the same time, some co-foundresses are non- or partially reproductive ("non-breeders”), and their role is currently unknown. I first tested the possibility that helping and breeding are divided, with non-helping females breeding, and non-breeders helping. In a lab experiment, I rejected this idea. Experimentally damaged domiciles were typically repaired by reproductive females, and less so by non- or partially reproductive individuals. To test whether non-helpers are an insurance workforce, I successively removed repairing females and found that non-helping females from the same domicile did not increase effort as a result, rejecting this hypothesis. Then I tested whether non-helpers were conserving energy waiting to breed. In a field experiment, I removed all other females, allowing either a helpful female or a non-helper to “inherit” her domicile. Isolated like this, non-helpers laid very few eggs compared to helpers or naturally occurring single foundresses, despite similar ovarian development. My findings show that labour was not divided: reproduction and helping covaried positively, probably depending on individual variation in female quality and intra-domicile competition. Non-helping females were neither an insurance workforce nor conserving energy waiting to breed. They are likely simply of poor quality, freeloading by benefiting from domicile maintenance by others. I hypothesize they are tolerated because of selection for indiscriminate communal brood care in the form of domicile repair.
README: Investigating the role of non-helpers in group living thrips
https://doi.org/10.5061/dryad.rjdfn2zmp
This dataset contains 4 data files in CSV format and 1 file of R code in Rmarkdown format.
Data
Note that in some cases these data files include individuals involved in studies unrelated to the current paper. These individuals are excluded from the code, with appropriate explanation.
Each data file corresponds to a different part of the linked paper, as follows:
- Are reproduction and domicile repair divided among foundresses?
- gilbert_2024_jae_dissection_data - fig 3 - dis.csv
- Are non-helping foundresses an insurance workforce for breeders?
- gilbert_2024_jae_sequential_removal_lab - figs 4 and 5 - xlab.csv
- Are non-helping foundresses waiting to breed themselves?
- gilbert_2024_jae_raw_data_removal_repair_tr.csv
- gilbert_2024_jae_removal_ovaries.csv
- Also uses some data from gilbert_2024_jae_dissection_data - fig 3 - dis.csv (see R code)
Code
All R code, and a reproduction of the results section of the paper in markdown format, are contained in the file entitled
- 2024-05-09 JAE Nonhelpers R code.Rmd
Description of the data and file structure
Field codes for all data files:
gilbert_2024_jae_1_dissection_data - fig 3 - dis.csv
In this dataset, each line represents one female, so multi-female domiciles appear on multiple lines. Some females/domiciles from unrelated experimental studies have been excluded. Other irrelevant cases are excluded in the R code.
- DATECOLL: Date domicile collected
- DATEDISS: Date female dissected
- ID.NEST: Domicile ID
- NEST.STAGE: Max stage of nest development (Building, No Eggs, Eggs, Active, Dispersed, Old)
- F.STATE: Female developmental stage (Teneral, Alate, Dealate) - all here are dealate, this is a subset of a larger dataset
- F.EXPT: Which experiment, if any, the female is assigned to. XLAB = sequential removal experiment; XR = removal experiment
- TREAT: treatment group to which the focal female is assigned, within the experiment described in F.EXPT; see main text and other datasets for context
- REPAIR: Repair latency coded as 3 level factor: 2 = repair; 1 = repair only after others removed; 0 = no repair
- PRONOT.50: Pronotum width in um, measured at 50x
- nestvol: Domicile volume (mm^3)
- chorion: Chorionated (i.e., mature) oocytes present in the ovary, true or false
- oocyte: Volume of developing oocytes in um3 (see Gilbert et al 2018, Scientific Reports, for the description of dissection and measurement protocols)
- chorvol: Volume of chorionated oocytes in mm^3
- oovol: Volume of developing oocytes in mm^3
- repro: Whether or not female is reproductive (i.e., has developing oocytes): true or false
- reprostate: Female reproductive state coded as a 3-level factor: Undeveloped, Developing oocytes, Mature oocytes
- repair: Whether or not the female engaged in repair: true or false
gilbert_2024_jae_2_sequential_removal_lab - figs 4 and 5 - xlab.csv
In this dataset, each line represents one female, so domiciles appear on multiple lines.
- NEST: Domicile ID
- ID: Female ID
- strands: Total number of strands laid by the female during the experimental observation period
- timein: Duration of the experimental observation period for that female (HH:MM)
- strandshour: Rate of strand deposition per hour (=strands/timein)
- timetop: Time spent as a primary repairer in the group during the experimental period
- timenottop: Time spent as subordinate (i.e., not primary) repairer in the group during the experimental period
- strandstop: Strands laid while primary repairer in the group during the experimental period
- strandsnottop: Strands laid while subordinate (i.e., not primary) repairer in the group during the experimental period
- strandshourtop: Rate of strand deposition per hour while primary repairer in the group during the experimental period
- strandshournottop: Rate of strand deposition per hour while subordinate (i.e., not primary) repairer in the group during the experimental period
- rank: repair rank within the group, on the basis of latency to begin repairing: 1 = top repairer, 2 = second repairer, etc.
- stage: Stage of domicile development (see Gilbert et al. 2013, Biol J Linn Soc)
- choro: Whether or not a female has mature oocytes (0 = no, 1 = yes)
- oocyte: Volume of developing oocytes, in um3 (this is converted to mm3 in the R script)
- chorvol: Volume of mature oocytes, in mm^3
- size: Pronotum width in um
- nestvol: Domicile volume in mm^3
- FOUNDRESSES: Number of foundresses in the nest
- relrank: Relative rank, i.e., repair rank (see "rank" column) scaled by the number of foundresses such that first repairer = relrank 0 and last repairer = relrank 1.
gilbert_2024_jae_3_raw_data_removal_repair_tr.csv
Each line of this dataset represents a domicile/nest, which received one of the treatments detailed in the accompanying paper (R, NR, CP, CS).
- IND: number of replicates
- ID: Domicile ID
- FNUMBER: Number of females initially present in the nest
- FBEHAVIOUR: Repair behaviour of females initially in the nest: H = helpful, U = unhelpful, M = male (never help), X = unknown
- TR.INITIAL: My initial division of nests into treatment groups (RH = remove helper, RNH = remove nonhelper, C = Control)
- tr: Final treatment group coding for statistical model (H = "helpful" = R group; U = "unhelpful" = NR group; C = control pairs (CP); AH = control singletons (CS).
- REMAINING: Behaviour of females in nest following treatment
- REPAIRTIME: Time to repair nest (days)
- REPCENS: Whether or not the nest was gone/destroyed before completely repaired
- GONE: Domicile disappeared during the experiment
- DESTROYED: Domicile was destroyed during the experiment
- STAGEAFTER: Nest stage 21 days after treatment (Building, No Eggs, Eggs, Active, Dispersed, Old)
- OFFSPRINGAFTER: Number of offspring in the nest 21 days after treatment
- NOTES: Notes
- X27.08.2013 (and columns thereafter): Action or observation on date. MA = Manipulation; NR = Not repairing; RE = Repairing; CO = Repair complete; GO = Gone; DE = Destroyed; BD = Blown down; COLL = Collected; X = post-collection.
gilbert_2024_jae_4_removal_ovaries.csv
In this dataset, each line represents one female, so domiciles appear on multiple lines. Data on the volume of developing/mature oocytes is attached to this dataset from the dissection data (File 1) in the R code.
- NEST: Domicile ID
- FF: Number of foundresses
- COMP: Repair behaviour of of females initially in domicile: H = helpful, U = unhelpful, M = male (who never help), X = unknown
- TREAT: My initial division of nests into treatment groups (RH = remove helper, RNH = remove nonhelper, C = Control, C1 = control singletons)
- REMOVE: Behavioural classification of individual(s) removed from nest: H = helpful, U = unhelpful, O = none removed, M = Male
- LEAVE: Behavioural classification of individual(s) left in nest: H = helpful, U = unhelpful, M = Male
- TR: Treatment applied to focal individual (R = removed at beginning of the experiment; L = left until the end of the experiment), but coding Control groups uniformly as C
- ST: Behavioural classification of the focal individual: H = helpful, U = unhelpful, C = control (i.e., unknown, could be either/any of the remaining individuals)
- PRESENT: Number of individuals present in the nest at the time of removal of the focal individual
- TR.INDIV: Treatment applied to focal individuals (R = removed at the beginning of the experiment; L = left until the end of the experiment), coding Control groups according to the actual treatment they received (i.e., control individuals were all L).
- ID.INDIV: An arbitrary ID for the individual within the nest, e.g. R1 is the first female to be removed, R2 is the second, and L1 is the first "left" female I dissected.
- STATUS.INDIV: Behavioural classification of a focal individual as for ST, but coding C groups according to the possible states (i.e., "HU" could be a helper or a non-helper).
- NOTES: Notes
Methods
Lab and field studies were conducted between January and October 2013, at a large patch of Acacia aneura, the host plant for D. aneurae, at the Bald Hills paddock (S 30° 57′ 39′; E 141° 42′ 18′′) near the UNSW Arid Zone Research Station, Fowlers Gap near Broken Hill, NSW, Australia (see Gilbert and Simpson 2013, Biol. J. Linn. Soc.). D. aneurae domiciles were identified and either collected or marked using coloured tape. I collected domiciles by hand and placed them into ziplock bags inside a cool box, moving them to a laboratory at room temperature within 12 h, and maintained them using protocols described in Gilbert & Simpson (2013). I examined the domiciles under a dissecting microscope.
Are reproduction and domicile repair divided among foundresses? In domiciles containing two or more females, I made a small tear in the wall (roughly 20% of the silk area), folded back the silk, and observed repair behaviour (defined as stretching strands of "silk" singly between phyllode surfaces) by the foundresses. After scoring in this way, all group members were removed and dissected under a microscope (see protocol below) for assessment of ovarian status. I also measured female body size to the nearest 20 µm (pronotum width at 50⨉ magnification).
Are non-helping foundresses an insurance workforce for breeders? In a subset of 19 domiciles, I counted the individual silk strands applied by each female while repairing the experimental damage. After 1 h I removed the first repairer to respond and observed the behaviour of the remaining female(s) over the subsequent 1 h period. Over successive 1 h periods, I removed one-by-one the repairers in the sequence that I saw them begin repairing and counted silk strands laid down by the remaining females. Removed individuals were dissected and scored for ovarian development as described below, and their pronotum width was measured.
Are non-helping foundresses waiting to breed themselves? In a field removal experiment using domiciles containing 2 or 3 females, I first categorised each female as “repairer” or "nonrepairer", as above: I slightly damaged the domicile wall, then observed the behaviour of the inhabitants for 3 h. I used a longer observation period of 3 h under field conditions where observation was more difficult, to be sure to identify nonrepairing females. After classifying, I removed all individuals from all domiciles. I then assigned domiciles randomly to treatment groups in which I reinstated to her original domicile either a repairer (R group, n=11) or a nonrepairer (NR group, n=8). In this way, I allowed (or forced) this female to “inherit” her domicile. Replacement was completed within 30 minutes of removal. All other females I dissected to assess reproductive status as described below. The remaining female I left in the domicile. I also created two control groups (CS, control singletons, and CP, control pairs). The CS group consisted of naturally occurring singly built domiciles (n=46), while the CP group consisted of domiciles naturally built by pairs of females (n=9). In the CP and CS groups, I performed the same experimental domicile damage before removing and immediately replacing all domicile inhabitants. After manipulation, I monitored domiciles for 21 days to assess (1) the time to repair the domicile, and (2) the number of offspring produced.
Time to repair domicile: Each day I visually categorised repair as “no repair”, “incomplete repair” or “complete repair”. “No repair” was where a negligible number of silk strands had been added and the damaged area remained substantially open to the environment. “Incomplete repair” was where repair had begun, but strands were sparse and perturbation of the phyllodes (e.g. by mild wind) would likely reopen the hole in the silk. “Complete repair” was where silk completely covered the damaged area, perturbation of the phyllodes would be unlikely to reopen the hole in the domicile wall, and/or the repaired wall resembled the original silk. I also recorded any instances of naturally occurring domicile damage (and its repair), destruction, or abandonment.
Offspring in domicile: After 21 days, I counted the number of offspring (eggs and larvae, live or dead) in each domicile, and dissected the female to examine her ovaries (see below). All individuals remaining in domiciles after the 21 d experimental period were also dissected as described below to assess reproductive status.
Assessing ovary status: I assessed ovarian development in all dissected individuals following Gilbert et al (2018, Scientific Reports). Foundresses were killed by immersing in 100% ethanol for 1 m and were dissected immediately in water. I recorded the number and volume to the nearest 20 µm at 50⨉ (π × length × (width/2)2), assuming eggs are an ellipsoid) of any developing oocytes, and also of any mature, chorionated eggs that were ready to lay, and summed the resulting volumes to give a total volume within each ovary. For analysis, oocyte and mature egg volumes were log-transformed after adding the minimum value in the dataset to all values.